Immunological properties of Fc receptor on lymphocytes. 6. Characterization of suppressive B-cell factor (SBF) released from Fc receptor-bearing B cells.

EA, i.e., antigen-antibody complexes are able to induce an antigen-nonspecific suppressive factor(s) from FcR⁺ B cells by binding on FcR. This factor, termed “suppressive B-cell factor (SBF)” was only effective on H-2 compatible, but not on H-2 incompatible spleen cells in an adoptive cell transfer system. Furthermore, SBF, prepared from B10.A (H-2^a) splenic FcR⁺ B cells, suppressed the adoptive primary response of B10.D2 mice (H-2^d), in addition to A/J mice (H-2^a) against DNP-DE, by the pretreatment of cells with SBF in vitro. Absorption with affinity columns demonstrated that active components) of SBF from C3H/He mice (H-2^k) was eliminated by both B6 anti-CBA (H-2^b anti-H-2^k) and B10.D2 anti-B10.BR (H-2^d anti-H-2^k), but not B10 anti-B10.A (H-2^b anti-H-2^a). In contrast, the suppressive activity of SBF was eliminated neither by anti-mouse Ig nor by a heat-aggregated human γ-globulin column. These results indicate that SBF contains a product coded by the right-hand side of H-2 gene complex, but does not contain Ig determinants nor FcR. Thus, it is conceivable that a compatibility of the right-hand side of H-2 gene complex is required for inducing effective suppression of spleen cells by SBF. SBF was considered to be a trypsin-resistant and heat-labile substance with a molecular weight of 30,000–63,000. The target cells for SBF were FcR^? B precursors, but not helper T cells.     

Acquisition of syngeneic I-A determinants by T cells proliferating in response to poly (Glu60Ala30Tyr10)

The T cell proliferative response in mice to the synthetic polymer GAT is under Ir gene control, mapping to the I-A subregion of the H-2 major histocompatibility complex (MHC). Antigen-dependent proliferation in vitro of in vivo GAT-primed lymph node cells can be inhibited by a monoclonal antibody to Ia-17, an I-A public determinant. Using this antibody for direct immunofluorescent analysis, T cells in GAT-stimulated proliferative culture are identified that express syngeneic I-A during culture. This expression is strictly antigen dependent, requires restimulation in vitro, and requires the presence of I-A-positive adherent antigen-presenting cells. T cells bearing I-A can be enriched by a simple affinity procedure, and I-A-positive cells separated on a FACS are shown to retain antigen-specific reactivity. The acquisition of I-A determinants by T cells under these culture conditions is not nonspecific. The Ia determinants borne by T cell blasts appear to be dictated by the I subregion to which the relevant Ir gene maps, and which codes for the Ia molecule involved in presentation of the antigen. Thus, (B6A)F1 (H-2b X H-2a)F1 LNC express I-Ak antigens when proliferating to GAT but not when stimulated by GLPhe, the response to which is under I-E subregion control. The relation of Ir gene function to Ia-restricted antigen presentation and self-Ia recognition is discussed.     

Specificity or affinity of cytotoxic T cells for self H-2K determinants apparently does not change between primary and secondary responses to ectromelia virus infection.

Lysis of virus-infected target cells by virus-specific cytotoxic T cells occurs where donors of T cells and targets share either H-2K or H-2D genes. The effect of four H-2K mutations on virus-induced antigens recognized by cytotoxic T cells from in vitro secondary response to infection was studied. B10.A(5R) cytotoxic T cells (which share the K end of H-2 with the mutant strains, except for the mutated gene(s)) efficiently killed virus-infected macrophage targets from mutant strains B6-H-2bg1 and B6-H-2bg2, were less effective against B6-H-2bh and did not appear to be cytotoxic for B6.C-H-2ba target cells. Conversely, B6-H-Ibg1 and B6-H-2bg2 cytotoxic T cells were more effective in killing virus-infected B10.A(5R) macrophages than B6-H-2bh and B6.C-H-2ba cytotoxic cells respectively. In addition, B6-H-2bg1 and B6-H-2bg2 cells appeared to be only slightly different from wild-type with respect to the interaction between virus-infected cells and T cells. The data obtained suggested that virus-induced antigenic patterns on infected B6.C-H-2ba (mutant) cells are more different antigenically from those on wild-type cells than are those on infected cells from the other mutants, B6-H-2bh, B6-H-2bg1 and B6-H-2bh2. This agrees with previous data using primary cytotoxic T cells and thus suggests that no detectable change in the affinity or specificity of cytotoxic T cell receptors occurs between primary and secondary responses to infection. These findings are also discussed in relation to the exclusion of T cells with receptors for H-2K determinants that are common to the mutants and wild-type, from the response to virus-infected self cells.     

The role of adherent cells in the secondary cell-mediated response in vitro to a natural poxvirus pathogen.

The role of adherent cells in an in vitro secondary response to ectromelia virus infection was investigated. Spleen cells from ectromelia-primed mice ("responder" cells) depleted of adherent cells by either carbonyl iron treatment, adherence to plastic or passage through cotton wool columns had a markedly decreased capacity to produce a secondary response, as indicated by decreased T cell-mediated cytotoxicity against virus-infected target cells, when cultured with virus-infected "stimulator" cells. The secondary response was restored by the addition of peritoneal cells from either normal or ectromelia-immune mice. Small numbers of peritoneal cells completely reconstituted the response within a certain dose range but larger numbers produced a marked inhibition of the response. Spleen cells were less effective in restoring the response. The peritoneal cells were not merely acting as additional, infected "stimulator" or antigen-presenting cells, since they could be added as late as 3 days after culture. Reconstituting activity was not affected by pretreatment with anti-theta serum and complement and cell separation studies showed that the activity was associated mainly with Ig-negative cells and that the active cell probably bears Ia antigens on its surface. These results indicate that the adherent cells involved are probably macrophages and that they act non-specifically to produce optimum conditions for the specific response of T cells.     

Development of responsiveness and incidence of bispecific cells as revealed by in vitro assessment of the maturation of mouse bone marrow cells.

The kinetics of the maturation of B cells were studied in adult thymectomized, lethally irradiated, and bone marrow-reconstituted mice. The spleen cells of the recipients were taken at various intervals after transfer and cultured in vitro with trinitrophenylated sheep erythrocytes (TNP-SRBC). The cultures were supplemented with either allogeneic culture supernatant or educated T-cell helper activity. Appearance of functional B cells in the bone marrow inoculum was assessed by the number of hemolytic plaque-forming cells (PFC) on the fourth day of culture. In a parallel series the frequency of surface Ig-bearing cells was determined by using fluorescent rabbit anti-mouse Ig serum. When helped by allogeneic culture supernatants, differentiating bone marrow cells showed a slower rate of maturation into functional B cells than when helped by specifically educated T cells. But in both cases the recovery of responsiveness reached the same level (number of PFC/10⁶ cells) as that of normal spleen cells 55 to 60 days after transfer. During the initial periods of recovery, bispecific PFC (reacting both to TNP and to native SRBC determinants) were detected regularly in numbers far exceeding their frequency in normal spleen cell cultures; in some experiments, the number of bispecific PFC amounted to as much as 30% of the total PFC, whereas, when the bone marrow cells completely recovered (sixtieth day), the frequency of bispecific PFC was similar to that found in normal spleen cell cultures. The number of surface Ig-bearing cells also reached a normal level after the fiftieth day following transfer. In general, the degree of functional maturation was better correlated with the cells bearing surface Ig in the shape of rings or caps, whereas the predominance of spot-bearing cells indicated immaturity of the population.     

The generation of effector T cells in influenza A-infected, cyclosporine A-treated mice

Specific effector T cells that mediate DTH to influenza virus were found to be formed in vivo in CsA-treated mice. The activity of these cells could only be measured when they were transferred into untreated naive mice. The cells mediating DTH were H-2 restricted in the I region of the MHC. When effector T cells that mediated DTH were transferred into CsA-treated recipients, no DTH activity could be detected. Influenza-specific cytotoxic T cells could not be detected in the spleens of CsA-treated mice given virus intravenously, even when drug treatment was started 3 days after virus administration. There was only a partial restoration of cytotoxic activity when spleen cells from CsA-treated infected mice were cultured in the presence of virus-infected stimulators. This seemed to indicate that Class I-restricted responses were more susceptible to CsA than the generation of Class II (or I-region-restricted) responses.     

The cell-mediated immune response to ectromelia virus infection. Secondary response in vitro: specificity, nature of effector and responder cells and requirements for induction of antigenic changes in stimulator cells.

An in vitro culture method was used to study secondary cell-mediated responses to ectromelia virus infection in mice. Infected, syngeneic spleen cells or peritoneal cells were efficient "stimulator" cells when cultured with "responder" cells obtained from mice infected with ectromelia 4-6 weeks previously. The kinetics of generation of cytotoxic cells in cultures were determined; a peak occurred on days 4-5. A separation procedure performed on the cytotoxic cells showed that activity was associated mainly with the Ig-negative subpopulation (T cell-rich) and that H-2 compatibility between cytotoxic cells and target cells was required. The secondary response was virus-specific, at the level of both induction and target cell lysis, at least so far as ectromelia and lymphocytic choriomeningitis (LCM) viruses are concerned. Seperation of responder cells prior to culture showed that a potent secondary response was generated with the Ig-negative (T cell-rich) subpopulation and only a weak response was observed when the responder cells were Ig-positive (rich in B cells). Infected stimulator cells did not appear to secrete significant amounts of soluble antigen into the medium over 4 days of culture. Thus, antigenic patterns effective in memory T cell stimulation may be largely associated with the surfaces of infected cells.Pretreatment of ectromelia virus with UV- or gamma-irradiation did not impair its ability to induce antigenic changes in stimulator cells. Stimulator cells treated with UV-or gamma-irradiated virus for 1 h and then immediately with pactamycin to inhibit further viral protein synthesis and replication were efficient stimulators, thus indicating that antigenic changes are induced very rapidly on the surface of stimulator cells after uptake of virus. These treatments are being used to further characterize the cellular requirements in the stimulator population.     

Lysis of uninfected and virus-infected cells in vivo: a rejection mechanism in addition to that mediated by natural killer cells

To examine the lysis of virus-infected cells in vivo, uninfected and lymphocytic choriomeningitis virus (LCMV)-infected L-929 cells were labeled in vitro with [125I]-iododeoxyuridine and implanted intravenously into mice. Natural cytotoxicity against both uninfected and virus-infected cells was demonstrated in normal uninfected mice, but LCMV-infected cells were cleared from the lungs and whole bodies more rapidly than uninfected cells. Treatment of L-929 cells with defective interfering LCMV inhibited standard virus synthesis and protected the target cells from enhanced in vivo rejection. The in vivo rejection was apparently mediated by a cellular constituent of the host immune response and not simply a result of virus-induced cytopathic effects on the target cell, as hydrocortisone acetate and cyclophosphamide each reduced rejection of both target cell types and eliminated the enhanced rejection of LCMV-infected cells. The enhanced rejection of LCMV-infected cells was not restricted by histocompatibility antigens, indicating that classic T-cell recognition was not involved in the lysis, and since the enhanced rejection of LCMV-infected cells was mediated by mice treated with cobra venom factor, complement was also not involved in the lysis. Although moderate levels of interferon (102 U/ml) were present in the sera and although there was a modest activation of natural killer (NK) cells in the lungs of LCMV-infected cell recipients but not uninfected cell recipients, the enhanced rejection of virus-infected cells did not appear to be NK cell mediated. Normal mice and mice depleted of NK cell activity by in vivo treatment with antibody to asialo ganglio-n-tetraosylceramide ( AGM1 ) rejected uninfected and LCMV-infected L-929 cells similarly. This antibody markedly inhibited the rejection of NK-sensitive YAC-1 cells. In addition to the natural cytotoxicity directed against virus-infected cells, a second nonspecific rejection mechanism appeared in response to treatment protocols which induced interferon. Polyinosinic-polycytidylic acid and infection with LCMV augmented in vivo rejection of both uninfected and LCMV-infected L-929 cells but eliminated the differential rejection of the virus-infected cells. Infection with LCMV also augmented the in vivo rejection of the NK-sensitive target cell, YAC-1. In vivo treatments with anti- AGM1 sera only moderately inhibited the elevated rejection of uninfected and LCMV-infected L-929 cells, indicating that the enhanced rejection of these target cells was predominantly mediated by a mechanism other than that mediated by NK cells.(ABSTRACT TRUNCATED AT 400 WORDS)     

Donor CD8+ T cells mediate graft-versus-leukemia activity without clinical signs of graft-versus-host disease in recipients conditioned with anti-CD3 monoclonal antibody

Donor CD8(+) T cells play a critical role in mediating graft-vs-leukemia (GVL) activity, but also induce graft-vs-host disease (GVHD) in recipients conditioned with total body irradiation (TBI). In this study, we report that injections of donor C57BL/6 (H-2(b)) or FVB/N (H-2(q)) CD8(+) T with bone marrow cells induced chimerism and eliminated BCL1 leukemia/lymphoma cells without clinical signs of GVHD in anti-CD3-conditioned BALB/c (H-2(d)) recipients, but induced lethal GVHD in TBI-conditioned recipients. Using in vivo and ex vivo bioluminescent imaging, we observed that donor CD8(+) T cells expanded rapidly and infiltrated GVHD target tissues in TBI-conditioned recipients, but donor CD8(+) T cell expansion in anti-CD3-conditioned recipients was confined to lymphohematological tissues. This confinement was associated with lack of up-regulated expression of alpha(4)beta(7) integrin and chemokine receptors (i.e., CXCR3) on donor CD8(+) T cells. In addition, donor CD8(+) T cells in anti-CD3-conditioned recipients were rendered unresponsive, anergic, Foxp3(+), or type II cytotoxic T phenotype. Those donor CD8(+) T cells showed strong suppressive activity in vitro and mediated GVL activity without clinical signs of GVHD in TBI-conditioned secondary recipients. These results indicate that anti-CD3 conditioning separates GVL activity from GVHD via confining donor CD8(+) T cell expansion to host lymphohemological tissues as well as tolerizing them in the host.     

Influence of IgH V-region genes on the growth kinetics of a murine B cell leukemia (BCL1)

The growth kinetics of an IgM-bearing B cell leukemia of BALB/c (Ig-1a) origin, designated BCL1, has been investigated in 2 allotype immunoglobulin (Ig) heavy (H) chain congenic strains, C.B-20 (Ig-1b) and C.AL-20 (Ig-1d), and an (H) chain recombinant strain, BAB-14 (Ig-1a/1b), that carries Ig-1a genes in the variable (V)-region and Ig-1b genes in the constant (C)-region. When large numbers (10(6) to 10(7)) of BCL1 cells were injected into these mice, leukemia, as measured by the appearance of leukemic cells in peripheral blood with subsequent mortality, did not occur in C.B-20, was delayed in C.AL-20, and progressed at the same rate in BAB-14 relative to BALB/c control mice. These results indicate that an immune response directed against an antigen encoded for by an H chain V region gene (idiotype or variable-region allotype) or linked gene (minor histocompatibility antigen) prevents the growth of the BCL1 leukemia in the C.B-20 mice. Tumor resistance appears to be due to T cell activity since adoptive transfer of such cells from C.B-20 tumor rejectors protected sublethally irradiation recipients from subsequent tumor challenge. Although H-2 restricted, anti-BCL1 cytotoxic cells were detected in C.B-20 mice challenged in vivo and restimulated in vitro with BCL1 cells, evidence is discussed that suggests that the resistance observed is not due to these effector cells. The resistance of allotype congenic mice to BCL1 was not absolute; a small inoculum (10(2)) was as lethal in C.B-20 and C.AL-20 as BALB/c mice. Thus, Ig-encoded cell surface antigens, although immunogenic, in no way ensure ultimate host survival.     

Rabbit T cells with and without Fc receptors

Earlier, indirect evidence for rabbit subpopulations differing in Fc receptors and in response to mitogen has been directly tested. T cells were purified from spleen suspension by removal of adherent cells, followed by removal of Ig-bearing cells on petri dishes coated with antibody, directed against the light chain allotype of Ig receptors. The purified cells were further fractionated by formation of EA rosettes and separation on Ficoll-Hypaque. T cells which lacked Fc receptors had a larger response when stimulated with Con A or PHA than did T cells which possessed Fc receptors. Both subpopulations responded more when irradiated nonadherent B cells were added to the mixture, but the extent of help was the same for both cell populations. T cells which contained both Fc receptor-bearing cells and cells which lacked the receptor had a response which was intermediate between that of the two separated subpopulations.     

Association of mouse adenovirus-induced cell surface antigen(s) with histocompatibility antigens

The topological relationship on the mouse adenovirus (M-Ad)-infected cell surface between virus-induced specific cell surface(s) antigens and serologically defined major histocompatibility antigens (H-2) was analyzed by the cap formation technique. Rhodamine-isothiocyanate (RITC)-labeled anti-S serum failed to stain the surface of virus-infected lymphoid cells which were pretreated with anti-H-2 serum and fluorescein isothiocyanate (FITC)-labeled anti-mouse immunoglobulin serum (anti-M-Ig) to cap the appropriate H-2 antigens. Conversely, the capping of the S antigens by pretreatment with anti-S followed by FITC anti-M-Ig serum induced cocapping of H-2 antigens. The β₂ microglobulins (β₂m) were also shown to be cocapped with S antigens by anti-β₂m or by anti-S serum. The S antigens, however, did not cocap with mouse-immunoglobulins or Thyl. 2 antigens on virus-infected B or T lymphocytes, respectively. To further elucidate the molecular relationship between S and H-2 antigens, radio-iodinated virus-infected cells were solubilized with Nonidet P40 (NP40) and S antigens were precipitated with anti-S serum. When the precipitates were analysed with sodium dodecyl sulfate Polyacrylamide gel electrophoresis, two major peaks were seen at positions of molecules of about 45,000 and 12,000 daltons both of which corresponded with molecules which were observed when NP40 extracts of virus-infected or uninfected cells were precipitated with anti-H-2 serum. Sequential immunoprecipitation analysis of infected cell extracts showed that S antigens were coprecipitated with either H-2K or H-2D antigens. These results suggest that the S antigens are somehow associated with H-2K or H-2D antigens separately.     

Abelson virus-transformed lymphocytes: null cells that modulate H-2.

A-MuLV-transformed lymphoid cells from Balb/c mice had the properties of null lymphocytes. They did not secrete Ig and all but one did not have detectable cell-associated Ig; one line synthesized, but did not secrete, the mu chain of IgM. The cells expressed H-2D and H-2K, but not H-21 histocompatibility antigens or theta-antigen; they had Fc receptors. Most cell lines grew to form donor cell tumors after inoculation into (Balb/c X C57B1/6)F1 mice. The tumor cells have more H-2Dd than cells passaged in vitro. Cell lines carried in vitro progressively lost H-2Dd. A line in which 5-30% of the cells were lysable by anti-H-2Dd was cloned; all eleven clones had H-2Dd (13-69% lysable) demonstrating that H-2 modulates in vitro. A clone with little H-2Dd (10-15% lysable) was tumorigenic even after treatment with anti-H-2Dd sera; at least 50% of the tumor cells were lysed by anti-H-2Dd. Thus A-MuLV-transformed lymphocytes modulate H-2 in vivo to higher levels and in vitro to lower levels.     

Functional heterogeneity among CD4+ encephalitogenic T cells in recruitment of CD8+ T cells in experimental autoimmune encephalomyelitis

Inoculation of Lewis rats with live or attenuated (irradiated or paraformaldehyde-fixed) CD4+ encephalitogenic T cells (S1 line) protects the recipients from transferred experimental autoimmune encephalomyelitis (tEAE) induced by S1 cells. A CD8+ T lymphocyte population specifically activated against the EAE-inducing S1 cells can be readily isolated from the lymphoid organs of pretreated animals. We show, in the present study, that encephalitogenic T cell lines derived from Lewis rats differ in their ability to induce resistance against tEAE in vivo and to stimulate CD8+ cell proliferation in vitro. We also demonstrate that the S19 line of encephalitogenic T cells, in combination with myelin basic protein (MBP), can stimulate CD8+ cell proliferation in vitro. The CD8+ cells generated in this way strongly suppress MBP-specific T cell proliferation in vitro. This combined effect of T cells and MBP was also evident in vivo. Neither S19 cells nor MBP alone induced resistance against S19-mediated tEAE, rather coinjection of these cells and MBP was required. Our results suggest that resistance to EAE is mediated by distinct populations of encephalitogenic T cells that activate Ts cells through different mechanisms. In some instances, both autoreactive T cells and their relevant autoantigen(s) may be needed to activate Ts cells in vivo.     

Differential effect of hybrid resistance on the localization of virus-immune effector T cells to spleen and brain

The hybrid resistance (Hr) effect operates in the lymphocytic choriomeningitis (LCM) in vivo transfer model to inhibit both the level of cytotoxicity T lymphocyte (CTL) generation in spleen and the induction of inflammation in cerebrospinal fluid (CSF). The effect is seen when LCM virus-immune T cells that are homozygous for H-2D ^b are injected into virus-infected, immunosuppressed recipients that are heterozygous for this allele, or into radiation chimeras that express an appropriate F₁ phenotype. Evidence that Hr to T -cell transfer is cell-dose-dependent and tends to diminish with age was found in both chimeric and normal F₁ mice. Inhibition of the capacity of injected T cells to cause meningitis is a more sensitive measure of Hr than is the further stimulation of CTL effectors in recipient lymphoid tissue. The injection of large numbers of H-2^b virus-immune T cells into (H-2 ^k X H-2 ^bF₁H-2 ^k) virus-infected recipients did not induce any cellular extravasation into CSF, though potent H-2^b-restricted CTL effectors were generated in recipient spleen. Evidence of minimal inflammatory process was found in one experiment where these chimeras were given a comparable dose of (H-2 ^b X H-2 ^d)F₁ immune spleen cells. Development of this Tcell-mediated immunopathological process depends essentially on the expression of the appropriate H-2 restriction element on radiation-resistant host cells which, in this case, presumably constitute part of the physiological barrier between blood and CSF.     

Differential susceptibility of cells expressing allogeneic MHC or viral antigen to killing by antigen-specific CTL

CD8(+) cytotoxic T lymphocytes (CTLs) generated by immunization with allogeneic cells or viral infection are able to lyse allogeneic or virally infected in vitro cells (e.g., lymphoma and mastocytoma). In contrast, it is reported that CD8(+) T cells are not essential for allograft rejection (e.g., heart and skin), and that clearance of influenza or the Sendai virus from virus-infected respiratory epithelium is normal or only slightly delayed after a primary viral challenge of CD8-knockout mice. To address this controversy, we generated H-2(d)-specific CD8(+) CTLs by a mixed lymphocyte culture and examined the susceptibility of a panel of H-2(d) cells to CTL lysis. KLN205 squamous cell carcinoma, Meth A fibrosarcoma, and BALB/c skin components were found to be resistant to CTL-mediated lysis. This resistance did not appear to be related to a reduced expression of MHC class I molecules, and all these cells could block the recognition of H-2(d) targets by CTLs in cold target inhibition assays. We extended our observation by persistently infecting the same panel of cell lines with defective-interfering Sendai virus particles. The Meth A and KLN205 lines infected with a variant Sendai virus were resistant to lysis by Sendai virus-specific CTLs. The Sendai virus-infected Meth A and KLN205 lines were able to block the lysis of Sendai virus-infected targets by CTLs in cold target inhibition assays. Taken together, these results suggest that not all in vivo tissues may be sensitive to CTL lysis.     

Transfer of agammaglobulinemia in the chicken. I. Generation of suppressor activity by injection of bursa cells

Spleen cells from adult agammaglobulinemic (bursectomized) chickens taken 1 to 3 weeks after an injection of histocompatible bursa cells can inhibit the adoptive antibody response to B. abortus of normal spleen or bursa cells in irradiated recipients. Spleen cells from Aγ chickens not injected with bursa cells generally do not. Moreover, bursectomized chickens which have been reconstituted with spleen cells within the first week after hatching do not respond with suppressor cell formation upon bursa cell injection. This apparent “autoimmunization” with bursa cells induces suppressor T cells which are only minimally sensitive to treatment with mitomycin C or to 5000 R γ irradiation. The suppressor activity is neither induced nor potentiated by concanavalin A in vivo. It is much stronger in spleen than in thymus cells and appears to be macrophage independent and to require intact cells. The cell component which stimulates the suppressor activity is more pronounced on bursa than on spleen cells, and is at most present to a very limited extent on bone marrow, thymus, or peritoneal exudate cells. It is better represented in comparable cell numbers of Day 17 than of Day 14 embryonic bursa. The inducing cell component is present in the membrane fraction of disrupted bursa cells. Immunization with bursa cells from B locus histoincompatible chickens leads to suppressor activity against histocompatible bursa cells. Although the removal of Ig-bearing cells from bursa greatly diminishes its immunizing capacity, injection of serum IgM and IgG does not induce suppressor cells. It is suggested that tolerance to a B-cell antigen is lacking in adult Aγ chickens, resulting in an autoimmune response upon exposure to B cells. The B-cell antigen may be a cell surface-specific form of Ig, a complex of Ig and a membrane component, or a differentiation antigen which appears simultaneously with Ig during ontogeny.     

The effects of Muramyldipeptide (MDP) in cell-mediated immunity

Summary N-acetylmuramyl-l-alanyl-d-isoglutamine (MDP) was tested in cell-mediated systems. A preparation of MDP, which yielded comparable activity to Freund's complete adjuvant in a humoral response against bovine serum albumin, was used to examine the degree of correlation between in vitro and in vivo models of cell-mediated immunity: (a) The proliferative T cell response in vitro was found to be most strongly enhanced by MDP at low antigen concentrations. The stimulation indices (SIs), however, were only enhanced at very low antigen concentrations because of a mitogenic effect of MDP in the absence of any added antigen. In vivo the proliferative response was measured in a graft-versus-host reaction where MDP caused a nonspecific (systemic) proliferation. In a host-versus-graft situation, however, MDP significantly enhanced the local proliferative response, besides causing an increased systemic background proliferation. (b) The cytotoxic T cell response in vitro was enhanced with suboptimal and optimal antigen concentrations; with supraoptimal antigen concentrations a strong decrease in lytic activity was observed. In vivo, MDP enhanced the cytotoxic activity of peritoneal exudate cells in the same allogeneic system (H-2^b anti H-2^a) as the one used in vitro. This enhanced activity did not, however, enhance adoptive protection in the immunoincompetent host. (c) Cytotoxic T memory function was unaffected by MDP, both in an in vitro system using subcellular material to elicit the cytotoxic response and in vivo, when an adoptive transfer system was used to assay T memory cells for their protective capacity against tumor in the immunoincompetent host. (d) Antibody-mediated cell cytotoxicity was slightly suppressed when MDP was present in vitro; in vivo-pretreated spleen cells exhibited enhanced activity, but only at low antibody concentrations where a macrophage activity was superimposed on the K cell activity. (e) Macrophages could be activated both in vitro and in vivo to kill tumor cells effectively.     

Antiviral protection by CD8+ versus CD4+ T cells. CD8+ T cells correlating with cytotoxic activity in vitro are more efficient in antivaccinia virus protection than CD4-dependent IL.

T cell-mediated protection against a recombinant vaccinia virus was evaluated in mice with respect to the relative contributions of CTL vs that of T cell-dependent IL and of CD4+ cells. H-2b mice primed with the wildtype of vesicular stomatitis virus serotype Indiana (VSV-IND wt) mount an in vitro measurable cytotoxic response against the nucleoprotein (NP) of VSV-IND and are protected against a challenge infection with a vaccinia-VSV recombinant virus expressing the NP of VSV-IND (vacc-IND-NP). Their protective mechanism was highly susceptible to in vivo depletion of CD8+ T cells, but resistant to CD4+ depletion or treatment with anti-IFN-gamma and anti-TNF-alpha. Surprisingly, also VSV-CTL nonresponder H-2k mice were protected against a challenging infection with vacc-IND-NP when primed with VSV-IND wt. In contrast to the CTL responder H-2b mice, this protection was highly susceptible to CD4+ T cell depletion and to anti-IFN-gamma or anti-TNF-alpha treatment, but resistant to CD8+ T cell depletion. Antibodies were not responsible because they failed to transfer protection; in contrast CD4+ T cells conferred significant protection. VSV-CTL responder H-2b and nonresponder H-2k mice were protected almost equally well against a challenge dose of 10(3) pfu vacc-IND-NP inoculated intracerebrally. However, after intracerebral challenge with 5 x 10(6) pfu vacc-IND-NP, the CTL nonresponder mice died, whereas the CTL responder mice eliminated the virus by day 5. These results collectively show that CD4+ T cell-dependent IL may mediate antiviral protection, but their efficiency is relatively weak compared with CD8-mediated protection correlating with cytotoxic activity in vitro.     

Requirements for stimulation of T cell responses against virus-infected cells: nature of ectromelia virus-infected cells capable of stimulating cytotoxic T cells in a secondary response in vitro.

The nature of infected stimulator cells in the in vitro secondary cytotoxic T cell response to ectromelia infection was investigated. It was found that macrophages were better stimulator cells than spleen cells. B cells (Ig-positive cells) were superior to T cells (Ig-negative cells) both on a relative proportion and on a cell-to-cell basis. Concanavalin A and lipopolysaccharide-stimulated lymphocytes were also effective stimulator cells but appeared to be slightly inferior to spleen cells. Spleen cells depleted of Ia-positive cells were markedly inferior to normal spleen cells as stimulators. It was also found that primary and secondary cytotoxic T cells were largely Ia-negative. These findings are discussed in relation to the likely events during T cell responses to infection in vivo.