Mucosal immunoregulation: environmental lipopolysaccharide and GALT T lymphocytes regulate the IgA response

In this review, we have emphasized: 1) bacterial lipopolysaccharide (LPS) involvement in IgA responses to orally administered thymic-dependent (TD) antigens; 2) characterization of Peyer's patch (PP) lymphoreticular cells; and 3) gastrointestinal immunization with gram negative pathogens and anti-LPS immunity to infection. Gut LPS, which interacts with PP lymphoreticular cells, is a major determinant for host responses to orally administered TD antigens. Bacteroides species are the principal microflora present in the gastrointestinal tract and our studies with phenol-water LPS extracts from Bacteroides fragilis indicate that both polysaccharide and lipid A activate lymphoreticular cells. The B. fragilis lipid A moiety, like that derived from E. coli and Salmonella LPS, induces B cell mitogenic responses in cultures from LPS responsive mice, but does not stimulate C3H/ H3J B cells. The inability of lipid A to stimulate gut-associated lymphoreticular tissue (GALT) cells of C3H/HeJ mice results in the induction of greater T helper cell activity in this tissue in response to orally administered TD antigens and ultimately results in an elevated IgA response pattern. Murine PP contain accessory cells (approximately 1% dendritic cells and 6-8% macrophages) and lymphocytes T (35-38%) and B (40-42%). Recent studies with antigen-specific T cell clones from C3H/ H3J PP have resulted in the isolation of IgA isotype-specific T helper cells (PP Th A cells). PP Th A cells are antigen-specific, bear Fc alpha receptors, and require H-2 histocompatibility with B cells for helper activity. PP Th A cells most effectively collaborate with surface IgA (sIgA)-bearing B cells (IgA committed B cells) for IgA isotype responses. Other studies have shown that PP dendritic cells and T cells form clusters when stimulated in vitro with sodium periodate and that these clusters promote polyclonal IgA responses in B cell cultures. Polyclonal IgA responses in cultures containing PP cell clusters from C3H/ H3J mice are considerably higher than those in identical cultures from LPS responsive mice. In other studies, the environmental influence on GALT B cells and their resultant commitment to IgA isotype is under investigation. CBA/N, X-linked immunodeficient (xid) mice possess an immature splenic B cell population which cannot respond to thymic-independent class-2 (TI-2) or certain TD antigens. However, GALT B cells of xid mice possess a mature Lyb-5+ B cell subpopulation capable of both TI-2 and TD responses.(ABSTRACT TRUNCATED AT 400 WORDS)     

Immunoregulation in the Peyer's patch microenvironment. Cellular basis for the enhanced responses by the B cells of X-linked immunodeficient CBA/N mice

The Peyer's patches (PP) of X-linked immunodeficient (xid) CBA/N and hemizygous (CBA/N X DBA/2)F1 (CDF1) male mice contain a B cell subpopulation that expresses the Lyb-5 maturational marker and is responsive to type 2 and T cell-dependent antigens in vitro, a B cell phenotype which is absent from the spleens of xid mice. Experiments reported here show that xid spleen B cells co-cultured with B cell-depleted PP cells from xid mice differentiated into specific plaque-forming cells in response to trinitrophenyl-Ficoll (type 2) and sheep erythrocytes (T cell-dependent). Two cell types were involved in this normalization of xid B cell responses. An accessory cell activity present in the PP, but not the spleens, of both CDF1 male (xid) and CDF1 female (normal) mice was required for the response to either the type 2 or T cell-dependent antigens. In the presence of this PP accessory cell, T cells from the PP of either xid or normal mice supported responses to both classes of antigens. In contrast, T cells from the spleens of xid mice did not support the response to trinitrophenyl-Ficoll, although the splenic T cells from normal mice did synergize with PP accessory cells in allowing plaque-forming cell development by xid B cells to this type 2 antigen. The xid PP T cell activity required for the type 2 response by xid B cells was present in the Ly-1+, Lyt-2- subpopulation, and the xid PP accessory cell activity was provided by an enriched population of dendritic accessory cells. These results demonstrate the the lymphoreticular cells comprising the PP microenvironment provide effective support for the differentiation of xid B cells in response to type 2 and T cell-dependent antigens.     

Isotype-specific immunoregulation. Systemic antigen induces splenic T contrasuppressor cells which support IgM and IgG subclass but not IgA responses

In the present study, we have isolated and characterized the Lyt-1+, -2- T contrasuppressor (Tcs) cells from mice systemically primed with SRBC. Adoptive transfer of splenic Tcs cells from these mice abrogates oral tolerance and supports IgM and IgG anti-SRBC plaque-forming cell (PFC) responses; however, unlike the responses seen after transfer of Tcs cells derived from orally primed mice, low IgA responses were seen. Mice systemically primed with lower SRBC doses (0.01 to 1%) exhibited contrasuppression only within the L3T4- T cell subset, whereas mice primed with a high dose of SRBC (10%), harbored Lyt-1+, -2- Tcs cells in both the L3T4+ and L3T4- subsets. Both the L3T4- and L3T4+ Tcs cell subsets supported IgM and IgG responses when adoptively transferred to orally tolerized mice, and when added to tolerized spleen cell cultures. Splenic Tcs cells from systemically primed mice supported mainly IgG1 and IgG2b subclass anti-SRBC PFC responses, a pattern also seen with Tcs cells derived from orally primed mice. Both L3T4+ and L3T4- Tcs cells from systemically primed mice exhibited well established characteristics of contrasuppressor cells including binding to Vicia villosa lectin and expression of I-J. The splenic effector Tcs cells which support IgM, IgG1 and IgG2b anti-SRBC PFC responses are antigen-specific, since both L3T4- and L3T4+ Tcs cells from spleens of mice primed with 10% SRBC reverse tolerance to SRBC, but not to horse erythrocytes (HRBC). Further, both L3T4- and L3T4+ Tcs cells from HRBC-primed mice reverse tolerance to IgM and IgG anti-HRBC, but not to anti-SRBC responses. Isolation of T3-positive Lyt-1+, -2- and L3T4- Tcs cell subsets by flow cytometry followed by adoptive transfer, showed that effector Tcs cells express T3 and presumably contain an Ag-R (TCR-T3 complex). These studies show that systemic priming with heterologous RBC induces splenic Ag specific Tcs cells in a dose-dependent manner, which support IgM and IgG subclass responses, but not IgA responses.     

Murine bone marrow IgA responses to orally administered sheep erythrocytes

Specific immunization protocols have been established for the induction of murine bone marrow IgA responses to the T cell-dependent (TD) antigen sheep red blood cells (SRBC). Systemic immunization, either i.p. or i.v., followed by a second injection, induced splenic IgM and IgG responses and a bone marrow IgM response. No significant IgA responses were observed in either lymphoid tissue compartment. Oral immunization with SRBC by gastric intubation for 2 days, followed 1 wk later by an i.p. injection of SRBC resulted in a splenic IgA plaque-forming cell (PFC) response, but did not elicit a bone marrow IgA response. Repeated daily gastric intubation of SRBC to C3H/HeN and C3H/HeJ mice led to the previously reported pattern of systemic unresponsiveness in C3H/HeN mice and good anamnestic type IgM, IgG, and IgA splenic anti-SRBC PFC responses in the C3H/HeJ strain upon parenteral challenge. Oral administration of SRBC for 14 days to C3H/HeN mice, followed by systemic SRBC challenge, resulted in diminished splenic PFC responses of all isotypes, whereas gastric intubation of SRBC for 28 days led to complete systemic unresponsiveness to antigen in C3H/HeN mice. Interestingly, the repeated oral administration of SRBC resulted in significant bone marrow IgA PFC responses upon i.p. challenge in both C3H/HeN and C3H/HeJ mouse strains. The bone marrow IgA responses were clearly dependent upon chronic oral exposure to SRBC, because gastric intubation with SRBC for 2 consecutive days/wk for 10 wk also induced bone marrow and splenic IgA anti-SRBC PFC responses in C3H/HeN mice. These results suggest that memory B cells reside in the bone marrow of orally immunized mice and can yield anamnestic-type responses to challenge with the inducing antigen. The memory cells may arise in the Peyer's patches of the gut and migrate to the bone marrow. The possibility that the bone marrow is a component of the common mucosal immune system in mammals is suggested by this study.     

Role of T Cells in the Mitogen-Induced Proliferation and Polyclonal Antibody Response of Murine B Cells

The effect of thymus-derived lymphocytes (T cells) on the responsiveness of bone marrow-derived lymphocytes (B cells) to bacterial lipopolysaccharide (LPS) was determined in in vitro experiments. Radiation resistant splenic T cells obtained from euthymic nu/+ mice increased the number of proliferating cells in the cultures of splenic B cells from athymic nu/nu mice even in a nonstimulated state. The radiation resistant T cells augmented significantly the responsiveness of B cells to LPS, as determined by an increase in proliferating cells and polyclonally induced anti-sheep erythrocyte (SRBC) IgM hemolysin plaque-forming cells (PFC). Addition of the T cells to B cell cultures not only augmented the responsiveness of B cells to suboptimal doses of LPS but also enabled B cells to respond to supraoptimal doses of LPS. As is well documented, the radiation resistant T cells were unable to induce the generation of anti-SRBC PFC in B cell cultures, unless the cultures were simultaneously stimulated with SRBC. Colcemid, a specific inhibitor of cell mitosis, blocked almost completely the exponential generation of anti-SRBC PFC in B cell cultures responding to SRBC with the aid of radiation resistant T cells. In contrast, colcemid did not affect the exponential generation of anti-SRBC PFC of a polyclonal nature in B cell cultures responding to LPS, either in the presence or absence of radiation resistant T cells.     

IgM-mediated enhancement of in vivo anti-sheep erythrocyte antibody responses: isotype analysis of the enhanced responses

The direct splenic anti-sheep erythrocyte (anti-SRBC) responses as well as the serum IgG1, IgG2a, IgG2b, and IgG3 anti-SRBC responses of CBA/CaJ mice were monitored 4-35 days after immunization with: (1) a suboptimal dose of SRBC, (2) a suboptimal dose of SRBC plus monoclonal IgM anti-SRBC, or (3) a high dose of SRBC. The direct plaque-forming cell (PFC) responses of mice in treatment group 2 were significantly higher than those in group 1 but similar to the responses in group 3. The serum anti-SRBC antibody responses of all IgG subclasses were significantly enhanced by IgM anti-SRBC and were generally even higher than the responses obtained with high doses of SRBC. The relative proportions of each serum IgG subclass were similar in all three groups. These data suggest that the enhancement of suboptimal anti-SRBC antibody responses by IgM anti-SRBC extends through IgM and all of the IgG subclasses and, further, that the isotype profile in antibody-enhanced responses is similar to that obtained with high doses of SRBC.     

Dose-dependent induction of immunologic enhancement and suppression after oral administration of antigen

The effects of feeding various quantities of a particulate antigen, sheep red blood cells (SRBC), on plaque-forming cells (PFC) in the spleen were determined. Mice were given various numbers of SRBC orally daily for 14 days, then injected with SRBC intravenously. Splenic IgA PFC responses to SRBC were enhanced in the mice fed 5 X 10(8) SRBC and splenic IgG PFC responses to SRBC were depressed in the mice fed 5 X 10(9) SRBC. Adoptive transfer experiments showed that enhancement of splenic IgA PFC responses and suppression of splenic IgG PFC responses were induced by the T-cell rich fraction from Peyer's patches (PP) and the spleen in 5 X 10(8) SRBC- and 5 X 10(9) SRBC-fed mice, respectively. Kinetic studies revealed that IgA helper cells or IgG suppressor cells appeared in PP 2 days after oral administration and 4 days after it in the spleen.     

Streptococcal serotype carbohydrate represents a novel class of type 2 antigen which is T-independent

Our studies reported here, fully characterize two unique type 2 antigens trinitrophenol (TNP)-M1 serotype carbohydrates (TNP-M1 g and TNP-M1 c) derived from streptococci, which fail to induce antibody responses in xid or neonatal mouse splenic cultures. These antigens generate brisk responses in normal spleen and Peyer's patch cell cultures of xid mice, all of which suggest that responses are elicited in the Lyb-3+, 5+ B subpopulation. The antibody responses to TNP-M1 g (and TNP-M1 c) are not dependent upon T cells. Furthermore, TNP-M1 carbohydrates induce anti-TNP plaque-forming (PFC) responses in cultures of small, resting splenic B cell populations without an added T cell requirement. Thus two categories of type 2 antigens are distinguished, one which requires T cells or derived factors, e.g., TNP-Ficoll, and a second TNP-carbohydrate antigen TNP-M1 that does not. Studies of the mitogenic and polyclonal B cell activation properties of M1 carbohydrates indicated that B cell proliferation is induced in both xid (Lyb-3-, 5-) and normal (Lyb-3-, 5- and Lyb-3+, 5+) splenic B cell subpopulations, but that differentiation to IgM synthesis fails to occur in the Lyb-3-, 5- B cell subpopulation. Thus M1 carbohydrates are unique probes that allow the selective induction of proliferation and differentiation of mature B cells that are presumably Lyb-3+, 5+. Because the M1 serotype carbohydrates induce polyclonal IgM synthesis and antigen-specific responses in only the mature B cell population in the absence of T cells, whereas TNP-Ficoll and other type 2 antigens require T cells or their derived factors, the Lyb-3+, 5+ B cell subpopulation may consist of a T cell-dependent and a T cell-independent compartment for responses to different carbohydrate type 2 antigens.     

T-cell help for the IgA response: the function of T cells from different lymphoid organs in regulating the proportions of plasma cells expressing various isotypes

Differential distribution of IgA-specific primed Lyt 2- T cells (TH) in favor of gut-associated lymphoid tissue (GALT) has been proposed to account for the high proportion of IgA-producing plasma cells at mucosal versus nonmucosal sites. We find, however, that GALT TH primed enterically with sheep red blood cells (SRBC) contain no more help for IgA responses than peripheral lymph node (PN) TH primed subcutaneously. Moreover, GALT TH are only poorly primed by enterically administered soluble protein antigen and therefore provide less help for all isotypes than PN TH primed subcutaneously with the same antigen. On the other hand, supernatants of GALT TH stimulated with concanavalin A (Con A) in vitro do help higher IgA:IgG plaque-forming cell (PFC) ratios in cultures with 2,4, 6-trinitrophenyl-SRBC (TNP-SRBC) than supernatants from PN and spleen, indicating that, when appropriately stimulated, GALT TH are capable of promoting relatively higher IgA responses than TH from other sources. Responses elicited by either SRBC-primed TH or splenic Con A supernatants in the presence of TNP-SRBC contained higher IgA:IgG PFC ratios than those elicited by linked recognition in the presence of haptenated soluble protein carrier.     

Heterologous antibody responses in mice with chronic T. cruzi infection: depressed T helper function restored with supernatants containing interleukin 2

Antibody production to sheep erythrocytes (SRBC) or hapten-conjugated SRBC (TNP-SRBC) was studied in mice with chronic Trypanosoma cruzi infections. Studies in vivo demonstrated that both IgM and IgG anti-SRBC responses were suppressed during chronic infection. Secondary IgG responses were suppressed regardless of whether the primary immunization was given before or after infection. The ability of cells from infected mice to provide help for antibody production was examined in vitro. Anti-SRBC responses were restored to cultures of whole spleen cells from infected mice by the addition of interleukin 2 (IL 2)-rich supernatants, indicating that these cells were capable of antibody production when sufficient help was provided. T cells from SRBC-primed infected mice were unable to provide significant help to normal B cell/M phi cultures for in vitro anti-TNP or anti-SRBC responses. The percentages of Thy-1+, Lyt-1+, and Lyt-2+ spleen cells were not significantly different between normal and infected mice. Anti-TNP and anti-SRBC responses were restored to cultures that contained T cells from infected mice and normal B cell/M phi by the addition of IL 2-rich spleen cell supernatants. The suppression of in vitro antibody responses in mice with chronic T. cruzi infections was associated with a lack of T cell help, which was provided by exogenous spleen cell supernatant.     

Immunoregulation in the rat: cellular and molecular requirements for B cell responses to types 1, 2, and T-dependent antigens

The requirements for primary in vitro plaque-forming cell (PFC) development in cultures of purified rat splenic B cells have been examined. Rat B cells were directly responsive to the type 1 antigen trinitrophenyl-Brucella abortus (TNP-BA), but both T cells and adherent accessory cells were required for B cell responses to the type 2 antigen TNP-Ficoll and the T cell-dependent (TD) antigen sheep erythrocytes (SRBC). However, the cellfree supernatants from concanavalin A-induced spleen cells of rat or mouse origin replaced the requirement for T cells and macrophages, and resulted in PFC development in response to TNP-Ficoll and SRBC and augmented PFC numbers in response to TNP-BA. Culture supernatants from induced murine T cell and macrophage cell lines were used to partially deduce the molecular requirements for the support of PFC development by rat B cells to these three antigens. Supernatants from the EL-4 (EL-4 sup) and B151 K12 (B15 sup) T cell lines augmented TNP-BA responses, suggesting that B cell growth factor II (BCGF-II) mediated this effect. An admixture of purified interleukin 2 (IL 2) and B15 sup supported PFC development to SRBC; indicating that IL 2, BCGF-II, and the T cell-replacing factor in B15 sup (B15-TRF) were sufficient to support this response. In addition, the IL 2 plus B15 sup-supported anti-SRBC PFC response was increased by the addition of an interleukin 1-containing fraction from the supernatant of the macrophage line P388D1. PFC development in response to TNP-Ficoll had the most stringent requirements and only occurred in the presence of EL-4 sup and B15 sup (IL 2, BCGF-I, BCGF-II, EL-TRF, B15-TRF). These data indicate that different cellular and molecular requirements exist for PFC development in response to types 1, 2, and TD antigens by rat B cells.     

Recombinant granulocyte-macrophage colony-stimulating factor restores deficient immune responses in mice with chronic Trypanosoma cruzi infections

Spleen cells from mice with chronic Trypanosoma cruzi infection generate a minimal plaque-forming response to SRBC in vitro. Addition of granulocyte-macrophage (GM)-CSF to cultures of spleen cells from chronically infected mice restored the plaque-forming cells (PFC) response to normal levels. Splenic adherent cells from chronically infected mice were deficient in their ability to reconstitute the PFC response of accessory cell-depleted normal spleen cells. Preincubation of splenic adherent cells from infected mice with GM-CSF restored their ability to reconstitute the PFC response of adherent cell depleted cultures. Ia Ag expression by splenic adherent cells from chronically infected mice was significantly lower compared to Ia Ag expression of cells from normal mice. Incubation of splenic adherent cells from chronically infected mice for 48 h with GM-CSF increased levels of Ia Ag expression to approximately those of uninfected mice. Peritoneal macrophages from infected mice produced IL-1 after incubation with GM-CSF at levels equivalent to those produced by similarly treated control macrophages. Spleen cells from chronically infected mice showed significant induction of IL-2 mRNA after GM-CSF treatment, and the addition of the anti-IL-2 mAb to GM-CSF supplemented cultures of spleen cells from infected mice blocked the restoration of the anti-SRBC PFC response. Thus, the ability of GM-CSF to restore the anti-PFC response to SRBC appears to involve the up-regulation of accessory cell function that includes increased Ia Ag expression and the induction of IL-1 production. These events also involve increased IL-2 production with resultant up-regulation of the response to SRBC by spleen cells from infected mice. Finally, it was shown that treatment of infected mice with rGM-CSF completely restored their depressed PFC production in vivo.     

Immunoregulation in the rat: ontogeny of B cell responses to types 1, 2, and T-dependent antigens

The development of rat B cells has been examined in neonatal and adult Fischer rats through the use of type 1 (TNP-Brucella abortus), type 2 (TNP-LPS(Ph), TNP-Ficoll) and T cell-dependent (TD) (SRBC) antigens. In vivo splenic PFC responses to TNP-Brucella abortus could be induced in newborn rats and by 12 days of age had reached adult levels. In contrast, the responses to the type 2 and TD antigens were 30% and 70%, respectively, of the adult levels at 30 days of age. Adoptive transfer of the B cells from neonatal and young rats into irradiated adult hosts demonstrated that the kinetics in the development of responses to these antigens (early for type 1, intermediate for TD, and late for type 2) were not due to limiting accessory cell or T cell help in immature rats. In vitro cultures of purified B cells from neonatal and adult rats were responsive to TNP-BA and TNP-LPS(Ph) but not to TNP-Ficoll and SRBC. However, the addition of spleen cell-derived Con A supernatant to the B cell cultures resulted in responses to all four antigens, which arose as a function of B cell age, with kinetics that were identical to those observed in vivo. Fluorescent staining of B cells from rats of various ages for cell surface IgM and analysis on the fluorescence-activated cell sorter (FACS) revealed that all splenic B cells from rats 4 days of age expressed a relatively high level of sIgM, and that a subpopulation that expressed a relatively low level of sIgM increased with age until it represented approximately 50% of the adult splenic B cells. Challenging Con A supernatant-supplemented cultures of FACS-prepared low sIgM+ and high sIgM+ cells revealed that B cells responsive to TNP-Ficoll were confined to the ontogenically late-arising low sIgM+ subpopulation but that B cells responsive to TNP-BA, TNP-LPS(Ph), and SRBC were present in both subpopulations.     

Selective impairment of B cell function by Neisseria meningitidis

Spleen cells from CBA/J mice infected with Neisseria meningitidis displayed depressed in vitro plaque-forming cell (PFC) responses to T-dependent (sheep red blood cell; SRBC) and T-independent (TNP-LPS, TNP-Ficoll) antigens. The inhibition was observed over a wide range of antigen concentrations. The decreased responsiveness of splenocytes from infected mice was due to a selective impairment of B-cell function since helper-T-cell activity was intact in infected mice as shown by the ability of T-enriched lymphocytes to cooperate with normal B-enriched lymphocytes in the generation of an anti-SRBC response, accessory macrophage function was preserved since adherent spleen cells from bacteria-injected mice were shown to produce normal or increased levels of IL-1 and were able to cooperate with normal non-adherent spleen cells in the generation of PFC against SRBC. Addition of peritoneal cells from normal animals or extraneous IL-1 both failed to restore normal PFC responses in cultures of splenocytes from infected mice. Finally, B-enriched lymphocytes from infected mice produced poor anti-SRBC responses when cultured with either Con A supernatant or T-enriched lymphocytes from normal or infected mice. Cell-mixing experiments failed to detect the presence of suppressor cells in cultures of unfractionated spleen cells or B-enriched lymphocytes from infected mice. Therefore, the immunological unresponsiveness associated with a Neisseria meningitidis infection was attributed to a meningococcus-induced defect(s) in B-cell function. In vivo polyclonal B-cell activation leading to clonal exhaustion did not play a major role in the depression of humoral responses since meningococcal infection induced little or no polyclonal Ig secretion.     

Effects of antigen-feeding on intestinal and systemic immune responses. III. Antigen-specific serum-mediated suppression of humoral antibody responses after antigen feeding.

Feeding mice sheep erythrocytes (SRBC) caused a significant decrease in splenic IgM antibody responses to SRBC given ip. Reduced IgM responses were due to a suppressor factor in the serum of fed mice rather than due to a lack of IgM antibody-forming cell precursors or to the presence of suppressor T cells. Although feeding initially primed mice to produce greater IgA and IgG anti-SRBC responses after SRBC challenge, the initial primed state was transitory. Mice fed SRBC for longer than 8 weeks had significantly reduced splenic IgG and IgA responses after SRBC challenge.Suppression of IgM responses by serum from fed mice was antigen-specific and not H-2 restricted. Serum from fed mice inhibited the induction of IgM anti-SRBC responses but did not block the expression of already established responses. The size of the suppressor factor and the ability to remove suppressor activity from serum by anti-mouse immunoglobulin suggested that suppression was mediated by antibody. However, the determinants against which the antibody was directed appeared to differ among batches of suppressor sera. Suppressor activity did not appear to be mediated by immune complexes, or soluble antigen. Oral feeding of antigen can have a marked influence on host systemic immune responses when the antigen used for feeding is subsequently administered parenterally. Thus, oral antigen administration may provide a way for specifically manipulating systemic immune responses in vivo. In addition, antigen-feeding may provide a means for producing transferable factors that suppress humoral antibody responses.     

Simultaneous induction of antigen-specific IgA helper T cells and IgG suppressor T cells in the murine Peyer's patch after protein feeding

The effects of feeding the dietary protein antigen, ovalbumin (OVA), on OVA-specific IgG and IgA immune responses involving Peyer's patches (PP) and mesenteric lymph nodes (MLN) were examined. Mice were administered soluble OVA by gastric intubation. One to 3 days later, PP, MLN, or spleen cells from these donor mice were adoptively transferred into normal syngeneic recipients. After two subsequent immunizations, spleens from the recipient mice were assayed for IgA and IgG anti-OVA plaque-forming cell (PFC) responses. None of the tissues from normal (unfed) mice had the inherent ability to alter recipients' IgG or IgA PFC responses. Within 1 day of OVA feeding, however, cells were generated in the PP that could augment recipients' IgA anti-OVA PFC responses and suppress IgG PFC responses. Three days after OVA feeding, these cells were present in MLN as well, and whereas the IgG suppressor cell also appeared to migrate to spleen, the IgA helper cell did not. The cells mediating antigen-specific IgG suppression and IgA help were both T cells but could be distinguished by surface phenotype. We therefore conclude that protein feeding induces differential, isotype-specific immunoregulation in gut-associated lymphoid tissues, part of which is mediated by an antigen-specific IgA helper T cell.     

Dendritic and B-cell function during antibody responses in normal and immunodeficient (xid) mouse spleen cultures

Dendritic cells (DC) act as accessory cells for T-dependent antibody responses in two ways. One is to induce a class of stimulating factors (BSF) which allow B lymphocytes to respond to heterologous red cells as antigen. xid DC induce the production of these BSF, but xid B cells totally lack responsiveness. A second mechanism of DC function applies to red cell and haptenated-protein antigens. Here DC, helper T lymphocytes, and antigen-specific B cells interact in discrete clusters. Then the B cells become responsive to BSF. xid DC are fully active in this pathway, and xid B cells develop significant (10-20% of control) responses. This partial reduction in xid B-cell function could be due to the poor viability of xid lymphocytes in vitro. There is a comparable reduction in xid polyclonal responses to alloreactive helper T blasts. The other severe deficit in xid involves antibody formation to haptens on polysaccharide carriers. This response in normal mice is not influenced by DC or by BSF. The only similarity between DNP-Ficoll and RBC plus BSF responses is that both utilize B lymphocytes that do not associate with DC-T clusters, even though helper cells for DNP-Ficoll and for RBC are present in the culture. We conclude that DC function is not altered in xid. The main deficit seems to be in a B-cell activation pathway that is shared by polysaccharide carriers and some but not all BSF, and/or in a B-cell subpopulation that does not interact with carrier-specific helper cells. We speculate that this B-cell alteration primarily involves the Ig delta-poor marginal zone subpopulation of splenic B lymphocytes.     

Acute hepatotoxin exposure effects lymphoid and accessory cell types in inbred mice

The effect of acute hepatotoxin exposure on in vivo and in vitro immune responses were investigated in inbred mice. Splenic anti-SRBC PFC responses were slightly enhanced by carbon tetrachloride or galactosamine administration 5 hr prior to immunization. Whereas splenic anti-SRBC PFC responses were slightly enhanced in euthymic mice exposed to carbon tetrachloride 5 hr prior to immunization, immune responses to the TI antigens, Fl-LPS, Fl-Ficoll, and TNP-LPS, were significantly suppressed. Athymic mice receiving similar hepatotoxin exposure elicited enhanced immune responses to the TI immunogens, thereby suggesting that the activities of B cells and macrophages are enhanced in treated animals and in euthymic mice, T suppressor cells are also activated. By admixture of purified B- and T-cell and macrophage populations from either carbon tetrachloride-treated or control animals, it was demonstrated that hepatotoxin exposure also induces suppressor T cells regulating immune responses to the T-dependent antigen, SRBC, and that macrophages from treated animals are more functional. Further, B-cell responsiveness is enhanced. In addition to these observations, an active factor could be demonstrated in sera from hepatotoxin-treated animals which augments immune responses to SRBC in normal mice and promotes immune responses to this antigen in athymic mice. These findings indicate that the effects of acute hepatotoxin exposure are multifocal, influencing the activity of lymphoid and accessory cells.     

Structural and serological studies of lipopolysaccharides of Citrobacter O35 and O38 antigenically related to Salmonella

Abstract Lipopolysaccharide (LPS) was administered into sheep red blood cells (SRBC)-primed mice, and the effect of LPS on SRBC-specific memory cells was investigated. Spleen cells from SRBC-primed mice which were injected with LPS exhibited much lower in vitro secondary plaque-forming cells (PFC) responses to SRBC than those from untreated SRBC-primed mice. The in vitro anti-SRBC response of the spleen cells to LPS was also reduced. The combination experiments of B cells and T cells from SRBC-primed mice which were injected with or without LPS demonstrated that the reduction of immune responses to SRBC after administration of LPS was caused by the defect of SRBC-specific B memory cells, but not T memory cells. B cell type rosette-forming cells (RFC) for SRBC markedly decreased after injection of LPS, while PFC as antibody-forming cells did not increase subsequently. Therefore, the reduction of RFC was not due to their differentiation into PFC. The lymphoid follicles in the spleens from mice injected with LPS were stained positively by in situ nick end labeling specific for fragmented DNA. A large percentage of Ig⁺ spleen cells from SRBC-primed mice which were injected with LPS was also stained positively. The injection of glucocorticoids into SRBC-primed mice induced similar reduction of B memory cells. It was suggested that LPS might induce apoptosis of B memory cells and regulate B cell memory in antigen-nonspecific manner.     

Expression of Lyb-5 and Mls determinants by Peyer's patch B lymphocytes of X-linked immunodeficient mice

Treatment of the Peyer's patch (PP) B cells from X-linked immunodeficient (xid) (CBA/N X DBA/2)F1 male mice with anti-Lyb-5 plus complement kills approximately 75% of these cells, although xid spleen B cells are unaffected. Cytotoxic depletion of Lyb-5+ cells renders the xid PP B cell population unable to generate an in vitro direct plaque-forming cell response to the TI-2 antigen TNP-Ficoll. In addition, the B cell-enriched population from the PP of xid (CBA/N X CBA/J)F1 male mice were strong stimulators of proliferation in an M1s-defined MLR, thereby demonstrating that they also express the M1s antigen(s). Two cell surface antigens associated with mature B cells are therefore expressed by xid PP B cells, suggesting that the TNP-Ficoll responsive cells in this population are mature B cell.