Novel vaccine strategies to T-independent antigens

T cell independent antigens do not require T cell help to induce an immune response, and are characterized by a lack of immunologic memory. These antigens can be divided into two classes, TI-1 or TI-2. TI-1 antigens, such as bacterial lipopolysaccharide, are potent B-cell mitogens, capable of non-specific, polyclonal activation of B cells. In contrast, TI-2 antigens can only activate mature B cells and consist of highly repetitive structures, such as capsular polysaccharides (CPS) from bacteria. Many vaccines currently in use consist of purified capsular polysaccharides from pathogenic bacteria such as Streptococcus pneumoniae and Neisseria meningitidis. These vaccines are efficacious in immune-competent adults, however, due to their TI-2 nature, are not effective in children <2 years of age. Converting polysaccharides into T cell dependent (TD) antigens, allows children, <2, to produce an effective immune response. This review focuses on various strategies used to convert the immune response to polysaccharide antigens from TI-2 to a TD response. Conjugate vaccines, anti-idiotypic antibodies, phage display library technology and DNA vaccines are discussed.     

Maturation of B cell subpopulations responding to phosphorylcholine

In this study, the order of appearance of B cell precursors responding to different phosphorylcholine (PC) antigens was investigated. Cells from neonatal BALB/c mice were transferred to male (CBA/N X BALB/c)F1 immunodeficient mice, and splenic fragment cultures were set up at different times after transfer. Because Xid F1 mice are unable to mount a primary anti-PC response, the time to prepare fragment cultures after cell transfer could be prolonged. This created an expanded maturation effect in which small differences in the response pattern of different precursor subsets are amplified. Splenic fragment cultures containing neonatal precursors were immunized with PG-TGG-HY (TD antigen), PnC (TI-2 antigen), or PC-TGG-LPS (TI-1 antigen), or with combinations of these antigens. The in vitro responses to these antigens were found to be additive, indicating the existence of different subpopulations. The detected precursors were also analyzed with respect to the T15 idiotype, which is the normally dominant idiotype of the response against PC in BALB/c mice. The analysis demonstrated a distinctly different maturation sequence of the three B cell subsets in which the order of appearance is: TI-1, TD, and TI-2 responding precursors. The T15 idiotype is expressed dominantly in all stages except the early stage of the TI-1 precursors.     

Role of CR2 in the human adult and neonatal in vitro antibody response to type 4 pneumococcal polysaccharide.

A number of studies have indicated that the complement receptor type 2 (CR2), which is the receptor for C3d, a degradation fragment of the complement component C3, regulates B lymphocyte activation and growth. Early reports have described that C3 regulates T cell-dependent (TD) antibody responses. The involvement of CR2 in the antibody response to T cell-independent type 2(TI-2) antigens was investigated because neonatal B cells, which are unresponsive to TI-2 antigens both in vivo and in vitro, express a significantly decreased level of CR2 as compared to B cells of adult donors. We utilized type 4 pneumococcal polysaccharide (PS4) as a model TI-2 antigen. In order to study the relationship between CR2 and the response to PS4, B cells were costimulated with PS4 and monoclonal antibodies (MAb) to CR2. HB5 and OKB7 anti-CR2 monoclonal antibodies enhanced the in vitro response of adult B cells to PS4, as measured in a PS4-specific spot-forming cell assay. Neonatal B cells could only be induced to respond to PS4 using high concentrations of OKB7 anti-CR2 MAb. The 8-mercaptoguanosine (8MGuo), an agent that can overcome the in vitro unresponsiveness to PS4 of neonatal B cells, increased CR2 expression on adult and neonatal B cells. Furthermore, 8MGuo synergizes strongly with anti-CR2 antibodies in augmenting the anti-PS4 antibody response. Data presented in this report provide evidence of CR2 involvement in the antibody response to PS4 and that the neonatal B cell unresponsiveness to TI-2 antigens may be due to the decreased expression of CR2.     

Generation of immune memory by haptenated derivatives of thymus-independent antigens in C57BL/6 mice. I. The differentiation of memory B lymphocytes into antibody-secreting cells depends on the nature of the thymus-independent carrier used for memory induction and/or revelation

It has been previously reported that trinitrophenylated lipopolysaccharide (TNP-LPS), a thymus-independent (TI)-1 antigen, elicits an anamnestic response to TNP in C57BL/6 mice. The ability of these mice to mount a secondary response to TI-2 antigens was analyzed. Priming with DNP-Ficoll or DNP-Dextran, both TI-2 antigens, resulted in an increased frequency of TNP-binding B lymphocytes. Evidence is presented that memory cell-induction by DNP-Ficoll does not require functional T cells. The differentiation into antibody-forming cells (AFC) of memory cells generated by DNP-Dextran or DNP-Ficoll cannot be obtained by a challenge with either antigen. There was no indication that the lack of a secondary response to TI-2 antigens was related to suppressive T cells interfering with memory expression. Memory cells induced by DNP-Dextran or DNP-Ficoll can nevertheless be activated by TNP-LPS. In contrast to the restricted sensitivity of TNP-memory cells generated by TI-2 antigens, TNP-LPS-induced memory cells are indifferently susceptible to TI-1 or TI-2 antigenic stimulation. These results are discussed in terms of memory B-cell subpopulations.     

Newborn and Wiskott-Aldrich patient B cells can be activated by TNP-Brucella abortus: evidence that TNP-Brucella abortus behaves as a T-independent type 1 antigen in humans

TNP-Brucella abortus (TNP-Ba) has been classified as a T-independent type 1 (TI-1) antigen in the mouse on the basis that it activates neonatal and CBA/N (X-linked immunodeficient) murine B cells in contrast to T-independent type 2 (TI-2) antigens. Therefore, it was of interest to determine whether human newborn and X-linked Wiskott-Aldrich syndrome B cells could be triggered by TNP-Ba. Previous studies had shown that human B cells from both these latter sources were relatively insensitive to stimulation with T-dependent and polysaccharide antigens (TI-2 in mouse). In this study, we show that TNP-Ba can trigger human cord blood B cells to differentiate into anti-TNP plaque-forming cells (PFC) in a hapten-specific and T-independent manner. The dose response and kinetics were similar to those previously seen with adult cells. The newborn responses, however, were lower than adult PFC responses. Precursor frequency and clone size analyses revealed that this lower response was not due to newborn cells containing fewer precursors but was the result of a reduced ability of these anti-TNP clones to expand. The ability of TNP-Ba to activate immature newborn B cells implies that this antigen can be used to assess B cell function in very young children. It also implies that TNP-Ba behaves as a TI-1 antigen in humans as well as in mice. This was supported by the finding that B cells from Wiskott-Aldrich patients, which were unreactive to polysaccharide antigens, were generally responsive to TNP-Ba. Therefore, it would appear that human newborn and Wiskott-Aldrich patients do possess a functionally competent B cell subset possibly equivalent to Lyb-5- immature murine B cells.     

Model system for study of cell interactions and mechanisms of immune response to T-independent antigens of type 2 in vitro

Cellular mechanisms of immune response to type 2 T-independent antigens (TI-2 antigens) are not fully elucidated up till now. In vitro system is the most convenient model for such studies. However, in vitro model requires relatively high cell density in the cultures. It hampers the study of minor lymphocyte subsets like CD5+ B-1 splenocytes, which play the main role in the immune response to TI-2 antigens. The use of cell mixtures of normal and immunodeficient congenic animals may help to resolve this problem. In this work, immune responses to TI-antigens of type 1 (TI-1 antigens) and to TI-2 antigens in vitro were studied in the mixtures of cells of normal (CBA) and congenic xid-mice (CBA/N). CBA/N mice lack CD5+ B-1 cells and do not respond to TI-2 antigens. Therefore, their splenocytes can be used as “filler” cells to create the optimal cell density in the cell cultures. Spleen and peritoneal cells of CBA mice and B-1 and B-2 lymphocytes isolated from peritoneum and spleen, respectively, were cultured in different proportions with CBA/N splenocytes with or without antigens. LPS and polyvinylpyrrolidone (PVP) were used as TI-1 and TI-2-antigens, respectively. Antibody- and immunoglobulin-forming cells (AFC and IFC, respectively) were determined by the ELISPOT method on the 4th day of cultivation. It was shown that CBA and CBA/N cells in mixed cell cultures retained their functional activity. Splenocytes of CBA mice responded to both TI-antigens. Splenocytes of CBA/N mice responded to TI-1 antigen (LPS) only. It means that in vitro B-1 cells play the main role in the immune response to TI-2 antigens, as they do in vivo. Thus, the developed model system can be used to study cellular mechanisms of immune response to TI-1 and TI-2 antigens in vitro.     

Cellular mechanism of primary anti-Thy-1 antibody responses in vitro induced by uniquely immunogenic thymocyte antigens

Thy-1 antigens are the only cell membrane antigens known to be able to induce primary antibody responses in vitro. We have shown that antigens from the thymocytes of mice and rats were highly immunogenic in cultures of murine spleen cells for the induction of Thy-1.1-specific plaque-forming cell responses, whereas antigens from other tissues, including brains and bone marrow, were poorly immunogenic, if at all. The thymocyte-specific Thy-1 immunogenicity was carried by disrupted cell membranes, and the specific activity for inducing responses was closely linked to Thy-1. We then tried to determine the mechanism of anti-Thy-1 antibody responses in vitro that were induced by the uniquely immunogenic thymocyte antigens. The thymocyte Thy-1 antigens behaved as T cell-independent class 2 (TI-2) antigens: they induced responses in athymic nude mice but not in CBA/N mice with a B cell defect. The apparent TI-2 responses to thymocyte Thy-1 did, however, require Thy-1+ cells in the responder, similar to anti-DNP-Ficoll responses. The full development of the anti-Thy-1 responses required the participation of splenic adherent cells (SAC). Nevertheless, the mechanism of the SAC dependency of anti-Thy-1 responses did not involve antigen presentation to lymphocytes by antigen-pulsed SAC, which contrasted with the finding that the presentation of antigen by live SAC to lymphocytes was indispensable for responses to DNP-Ficoll. The poor Thy-1 responsiveness of SAC-depleted spleen cells was fully restored by the addition of soluble factors (IL 1-like molecules) released from SAC into the culture, which did not replace the SAC-requirement of responses to DNP-Ficoll. It was concluded from these results that Thy-1 or Thy-1-linked structures on thymocyte membranes have an intrinsic activity to directly signal either TI-2 B cells or immature T cells, or both, for activation in the presence of soluble factors released from adherent accessory cells. This conclusion is discussed in relation to a hypothetical view that the thymocyte Thy-1 would physiologically mediate cell-to-cell interactions among special subsets of lymphocytes under thymic influence.     

Induction of antigen-specific proliferation in affinity-purified small B lymphocytes: requirement for BSF-1 by type 2 but not type 1 thymus-independent antigens

We report here the role of B cell stimulatory factors in the induction of antigen-specific proliferation of affinity-purified small B lymphocytes. TI-1 antigens such as TNP-LPS and TNP-BA induced proliferation of hapten-binding B cells in the absence of exogenous B cell stimulatory factors. TI-2 antigens such as TNP-Ficoll required the co-stimulator BSF-1 to induce antigen-specific proliferation, and this response could be augmented by IL 1. TD antigens such as TNP-OVA were unable to induce antigen-specific proliferation either in the absence or presence of B cell stimulatory factors, and showed an absolute activation requirement for carrier-specific helper T cells. No role for IL 2 or BCGF II could be found in the factor-dependent proliferative response of hapten-binding B cells to TI-2 antigens, either as primary co-stimulators or as modulators of the response obtained with TNP-Ficoll, BSF-1, and IL 1. In contrast, concentrations of IFN-gamma that were nontoxic for normal B cells and B cell hybrids effectively abrogated the proliferative response of affinity-purified cells to TNP-Ficoll, BSF-1, and IL 1. By all of these criteria, the B cell activation requirements of TI-2 antigens appear to be identical to those previously published for soluble anti-IgM antibodies.     

A reappraisal of "T-independent" antigens. II. Studies on single, hapten-specific B cells from neonatal CBA/H or CBA/N mice fail to support classification into TI-1 and TI-2 categories

Spleen cells from adult CBA/H or CBA/N mice, or from neonatal CBA/H mice, were fractionated on thin layers of fluorescein (FLU)-gelatin to yield FLU-specific B lymphocytes. A single cell, or small numbers ranging from 1 to 10, were cultured in 10-microliter microcultures together with various antigens and mitogens. The results were compared with those of bulk culture or limiting dilution cultures supported by thymus filler cells. B cell growth and differentiation-promoting conditioned media (BGDA) were added to some cultures. The CBA/N results gave no support to the commonly used classification of T cell-independent (TI) antigens into TI-1 and TI-2 categories. A typical supposed TI-1 antigen, FLU-LPS, strongly stimulated normal adult single FLU-specific B cells to proliferate and form antibody, but virtually failed to trigger CBA/N B cells of comparable antigen-binding avidity. The same was true of LPS or LPS plus dextran sulfate acting as mitogens. The allegedly TI-2 antigen FLU-Ficoll, although still triggering comparatively poor responses, was actually marginally more active than FLU-LPS. FLU-Brucella abortus (FLU-BA) + BGDA gave the best results with single CBA/N B cells, but still induced only 1.27% of cells to develop into antibody-forming clones vs 12.2% with CBA/H cells. The results obtained with single neonatal B cells also lent no support to the distinction between TI-1 and TI-2. Both "TI-1" and "TI-2" stimuli caused adequate proliferation, one "TI-2" antigen stimulating 23.2% of the cells. None of the antigens caused good antibody formation, however, probably because multivalent antigens can deliver signals impeding the differentiation of immature B cells. It is therefore suggested that the classification of TI-1 antigens into two subcategories be abandoned, at least for the time being.     

In vivo allogeneic effects: shift in the isotype profile of primary TI-2 responses in mice undergoing graft-vs-host reaction

We showed previously that primary responses to T-dependent (TD) and T-independent type 2 (TI-2) antigens were differentially affected by allogeneic effects induced in vivo during a graft-vs-host reaction (GVH). TD responses were greater than or equal to 80% suppressed, whereas the TI-2 responses were greatly enhanced, particularly the IgG component, which normally is very low. We have analyzed the IgG subclass distribution in primary responses of normal and GVH F1 mice in order to determine whether the strong T cell signals that occur during GVH reactions also induce shifts in the isotype profile. The effect of GVH on responses to TI-2 antigens was of particular interest because they are usually dominated by IgM and IgG3 classes in normal mice. We found a threefold to 10-fold increase in the PFC numbers of all four IgG subclasses in the response to TI-2 antigens, with an apparent shift from the usual IgG3 dominance to IgG1 in GVH mice. This IgG1 dominance was not found in serum antibodies where IgG3, IgG1, and IgG2b were equally expressed, although total IgG was increased greater than 20-fold. No isotype shift was found in either the TNP-KLH response, which was greater than or equal to 75% suppressed (IgG1 dominance was retained), or in the TI-1 response to TNP-Ba. The latter response was reduced (25 to 50%) in GVH mice and continued to be dominated by IgG2b/2a and IgG3. Unlike the unique isotype patterns found in primary responses, TNP-KLH primed mice challenged with TD, TI-1, or TI-2 antigens gave memory responses with identical isotype profiles that were dominated by IgG1 PFC. The role of T cells in B cell differentiation and isotype expression is discussed.     

Secretion and role of interleukin-1-like factor in the antibody response to dinitrophenyl dextran and other type 2 T-independent antigens

Splenic adherent cells (SAC) were found to produce a humoral factor when they were cultured with dinitrophenyl-dextran or some other type 2 T-independent (TI-2) antigens. The factor substituted adherent cells in in vitro antibody responses to TI-2 antigens, and acted in an antigen-nonspecific and H-2-nonrestricted manner. T cells were indicated not to participate in the production of the factor. The factor was eluted from a Sephadex G-75 column with interleukin-1 (IL-1) activity to promote a thymocyte proliferation response to phytohemagglutinin. The molecular weight of the factor was estimated to be 16,000 Da. Both activities of the factor were absorbed by LBRM-33-1A5 cells. These results indicate that SAC secrete IL-1-like factor on direct stimulation by TI-2 antigens and that the secretion of the factor represents a major function of SAC in the antibody response to these antigens.     

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)     

Anti-immunoglobulin antibodies. V. Age-dependent variation of clones stimulated by polysaccharide TI-2 antigens in 129 and MRL mice spontaneously producing anti-gamma-globulin antibodies

The nature of the immune response to two conventional polysaccharide thymus-independent (TI) antigens was investigated in two RF-producing mouse strains, the 129/Sv and MRL/1 pr, as well as in their normal congenic counterparts, 129/J and MRL +/+ animals. An age-dependent variation of clones specific for the TI-2 antigens bacterial levan (BL) and alpha 1, 3 dextran B1355 (Dex) was observed in 129/J mice. Surprisingly, the anti-BL and anti-Dex responses observed for young (1-mo-old) 129/Sv mice far exceeded those of their age-matched controls indicating an accelerated ontogenic development of the immune response to TI-2 antigens. A poor response was observed for both MRL +/+ and MRL/1 pr mice after immunization with BL. More importantly, MRL mice, unlike other H-2k, Igh.Ca strains, were unresponsive to Dex in CFA or saline. MRL mice, however, could respond to the T-dependent form of this antigen, Dex-KLH, suggesting that these mice lack the subset of B cells required to respond to TI-2 antigens. Finally, the most striking observation was the occurrence of isotype-specific RF subsequent to immunization with these antigens in animals prone to develop RF, as well as in aged animals that do not spontaneously produce RF.     

The role of complement receptor positive and complement receptor negative B cells in the primary and secondary immune response to thymus independent type 2 and thymus dependent antigens

Both complement receptor positive (CR+) and complement receptor negative (CR-) B cells have been shown to be involved in the primary immune response to PC-Hy (phosphocholine conjugated hemocyanin), a thymus dependent (TD) antigen which preferentially induces antibody secretion in Lyb-5+ B cells during a primary adoptive transfer assay. CR+ and CR- B cells also responded in a primary adoptive transfer assay to TNP-Ficoll, a thymus independent type 2 (TI-2) antigen which activates only Lyb-5+ B cells. When the secondary immune response to PC-Hy and TNP-Ficoll were analyzed, it was found that most of the immune memory to both antigens was present in the CR- B cell subset. The CR- B cell subset also dominated the secondary immune response to PC-Hy in immune defective (CBA/N X DBA/2N)F1 male mice. These data indicate that CR- B cells dominate the memory response in both the Lyb-5+ and Lyb-5- B cell subsets of normal and xid immune defective mice and suggest that Lyb-5+ and Lyb-5- B cells can be subdivided into CR+ and CR- subsets.     

Role of dendritic cells in the immune response to T-independent antigens of type 2

Dendritic cells (DC) belong to the most effective antigen-presenting cells. Their role in the presentation of thymus-dependent antigens and initiation of primary immune response is well known. At the same time, participation of DC in the immune response to T-independent antigens of type 2 (TI-2 antigens) is poorly explored. In this work, the ability of DC to initiate the immune response to a TI-2 antigen α(1→3) dextran (Dex) is investigated. Mouse bone-marrow-derived DC were generated by culturing the precursors with GM-CSF and then DC were pulsed by TI-2 antigens. The pulse induced DC activation, as was verified by an increase in the number of CD80 and CD86 positive cells. Uptake of FITC-labeled Dex was examined by flow cytometry. At a concentration of FITC-Dex of 100 μg/10⁶ cells, the number of DC binding the antigen (Ag) reached “plateau”. DC charged by TI-2 antigens were mixed with normal mouse splenocytes and cultivated in RPMI-1640 medium for 4 days. The numbers of antibody- and immunoglobulin-forming cells were determined by ELISPOT method. The mixtures of splenocytes and naïve DC not charged by the Ag were used as control. It was shown that the increase in the numbers of AFC and IFC under the influence of naïve DC did not exceed 20%. On the contrary, the addition of DC pulsed by the Ag increased specific immune response more than twofold. The data obtained point to the direct interactions of DC with TI-2 antigens. Pulsed DC present TI-2 antigens to mouse splenocytes and induce specific and polyclonal B-cell activation, i.e., possess immunostimulating activity.     

T cell dependence and factor reconstitution of in vitro antibody responses to TNP-B. Abortus and TNP-Ficoll: restoration of depleted responses with chromatographed fractions of a T cell-derived factor

In vitro anti-trinitrophenyl (TNP) antibody responses to TNP conjugates of killed Brucella abortus organisms (TNP-BA), an antigen previously designated as a type 1 thymus-independent (TI-1) antigen, are markedly diminished after vigorous depletion of T cells, as are the responses to the type 2 TI (TI-2) antigen, TNP-Ficoll. We, therefore, propose that these antigens be redesignated as type 1 and type 2, respectively, to reflect their T cell dependence but to differentiate them from classical T cell-dependent (TD) antigens. T cell-depleted responses to type 1 and type 2 antigens can be restored by the addition of a) EL4 supernatant, b) phenyl-sepharose-purified fractions of EL4 supernatant that are rich in interleukin 2(IL2), and c) pl 4.5-5.5 isoelectric focused (IEF) fractions of EL4 supernatant which are also rich in IL2 activity. Removal of IL2 activity from EL4 supernatant by absorption on IL2-dependent T cells substantially reduced its restorative ability. Whether the active principle in EL4 supernatant activity responsible for restoring responses to type 1 and type 2 antigens is IL2, and whether it acts directly on B cells or by acting on contaminating T cells, is unresolved.     

Ability of chicken B cells from different compartments to respond to TNP-Ficoll

The responsiveness of chicken B cells from various compartments to T-independent antigens was studied by immune transfers of spleen and bursa cells into immunosuppressed recipients. Bursa cells from 8- to 10-wk-old donors failed to respond to trinitrophenylated Ficoll (TNP-F) even when thymus cells or splenic T cells were added. Spleen cells from the same donors transferred responses, as judged both by anti-TNP plaque-forming cells (PFC) per spleen and serum anti-TNP titers. In contrast, responses to TNP-Brucella abortus (TNP-BA) were transferred at least as well as by bursa as by spleen cells. Rabbit anti-chicken T cell serum plus complement treatment of the spleen cells reduced their ability to transfer responses to sheep erythrocytes, but either did not affect or enhanced serum antibody responses to TNP-BA and TNP-F. In intact animals, responsiveness to i.v. injected TNP-F was found to develop slowly after hatching in the chicken. At the age of 2 and 3 mo, PFC/spleen on day 4 after TNP-F injection were only 20% and 40%, respectively, of the adult response. Thymectomy at hatching further delayed this development, resulting in 12% and 45% of the adult control response at ages of 3 and 4 mo. It is concluded that responsiveness to the TI-2 antigen, TNP-F, develops slower than that to the TI-1 antigen, TNP-BA, and is restricted to the splenic B cell compartment. In addition, this development appears to be faster in the presence rather than in the absence of the thymus. In view of the previously shown effect of thymus on bursa development, these data suggest that the maturation of TI-1 antigen (TNP-F)-respondent chicken B cells requires residence in both the bursa and spleen before the development of responsiveness to such antigens.     

Functional evidence for abnormal maturation within a B-cell subpopulation of NZB mice

NZB mice develop a systemic autoimmune disease and have a subpopulation of B lymphocytes that spontaneously produce excessive amounts of IgM. These abnormal B cells reside within a specific B-cell subset that is affected by the CBA/N defect. In normal mice, this B-cell subset acquires in vitro responsiveness to certain thymus-independent antigens (TI-2) relatively late in ontogeny. We compared the functional development of neonatal B cells from NZB mice to that of normal mice of the same H-2 type. The acquisition of in vitro responsiveness to the TI-1 antigen, TNP-LPS and the TI-2 antigens, TNP-Dextran, TNP-Ficoll, and FITC-Ficoll was examined. TNP-LPS could elicit a response from both normal and NZB neonates. In contrast, responses to the TI-2 antigens were elicited early in life (<1 week) only from or at a higher level from NZB neonates. However, an accelerated appearance of B-cell differentiation antigens was not detected in NZB neonates compared to normal strains. We conclude, therefore, that a maturation or triggering defect occurs in a small B-cell subpopulation of NZB mice very early in life.     

The mouse mutant "motheaten." II. Functional studies of the immune system.

Motheaten mice have normal levels of T lymphocytes but reduced levels of B lymphocytes. Those B cells that are present show an impaired proliferative response to B cell mitogens and no plaque-forming cell response to thymus-independent antigens. T lymphocyte function is also defective in motheaten mice, as assayed by the proliferative responses to T cell mitogens, and by the capacity to develop cytotoxic killer cells against allogeneic cells. Motheaten mice possess spleen cells capable of suppressing normal B cell responses to thymus-independent antigens. This suppressor cell is not sensitive to anti-Thy-1 antibody plus complement treatment but is partially removed by adherence on plastic. Overall, the motheaten mouse suffers a functional severe combined immunodeficiency of both B and T cells, even though these cells are present. We postulate that the inescapable lethality of the motheaten defect is due to the lack of immunocompetence during the critical developmental period before adulthood and perhaps to an autoaggressive component as well.     

Human cell membrane components dominant in T cell lineage: identification and characterization of human TL-like antigens.

Cell membrane components that contain beta 2-microglobulin were purified from cells of a human T cell-type leukemia cell line, HPB-ALL. They contained membrane components that have the same molecular size and the same subunit structure as HLA(A,B,C) antigens but are separable from the typical beta 2-microglobulin-containing cell membrane components, i.e., the HLA (A,B,C) antigens, by xenoantibody reagents. A sensitive radioimmunoassay was constructed for detection of the T cell membrane components. The assay revealed that the cell membrane components are expressed exclusively on cells of T cell-type leukemia cell lines among the human lymphoid cell lines tested, predominantly in thymus, among the human organs and tissues tested. They were not present on cells of human B cell-type cell lines or on cells of nonlymphoid organs and tissues. No alloantibodies directed to the T cell membrane components, the putative human homologues of mouse TL antigens, were found in any of the human tissue typing sera tested.