Restricted adult clonal profiles induced by neonatal immunization. Influence of suppressor T cells

Immunopathology of granuloma formation and fibrosis in schistosomiasis

In schistosomiasis the deposition of parasite ova within host tissues is the initial event in a complex pathophysiological cascade which is characterized by granuloma formation, and may terminate in fibrosis and related sequelae (Fig. 1). In spite of intensive study, the complex relationship between infection and morbidity remains poorly understood. In this article, Michael Phillips and Patrick Lammie review current concepts of the mechanisms of granuloma formation and its regulation in schistosome infections.

B-cell maturation in chimaeric mice deficient for the heat stable antigen (HSA/mouse CD24)

The murine differentiation marker heat stable antigen (HSA) is a GPI-anchored surface glycoprotein showing strong expression on immature B- and T-lymphocytes and gradually reduced expression during maturation. Although HSA has been suggested to be involved in adhesion and/or signalling, its function has not been clearly demonstrated so far. In order to elucidate the function of HSA, we analysed chimaeric mice that were generated by targeted disruption of both HSA alleles in ES cells. These mice contain normal numbers of peripheral B-cells and normal serum IgM and IgG titres of ES cell-derived allotype, demonstrating that HSA expression on B-cells is not an absolute requirement for their maturation. However, a reduction in immature B-cells in the bone marrow and an altered degree of bone marrow and blood chimaerism suggest that HSA expression influences the maturation of B-cells.

Effect of priming with a thymus-independent antigen on susceptibility to B-cell tolerance

The effects of priming on the susceptibility of B-cell subsets to tolerance induction have been tested in a model system in which anti-immunoglobulin (anti-Ig) has been employed as a surrogate for tolerogen. T-cell-depleted B cells were primed in vitro with fluorescein or trinitrophenylated Ficoll (a thymus-independent (TI) antigen) and then exposed overnight to anti-Ig to attempt to induce B-cell anergy. Primed cells were relatively resistant to this tolerance protocol and resistance was hapten specific. The dose response and kinetics suggested that this process was not due to receptor blockade or modulation, but was an active process. Moreover, this priming for resistance to tolerance was reproduced in vivo upon intraperitoneal treatment with haptenated Ficoll. Such in vivo priming for tolerance resistance was long-lasting and did not occur with a thymus-dependent priming protocol with fluoresceinated hemocyanin. These results are discussed in terms of TI priming to drive B cells into cycle and express novel functional and phenotypic properties.

Surface markers, heavy chain sequences and B cell lineages

A unifying theory of B cell development and lineage commitment is presented. There are two firmly established B lineages: cells which normally arise only from fetal sources and lack N insertions in their rearranged heavy chains; and N-containing cells which arise from adult bone marrow precursors (and perhaps from late fetal sources). Commitment to the expression of CD5 and the capacity for long-life (or self-renewal) are induced as a consequence of sIg cross-linking, typically by a repeating epitope, thymus independent type two antigen. Alternatively, activation resulting from cognate interaction with a helper T cell does not induce CD5 but results in lower expression of J11d. In this case activation occurs in the absence of sIg cross-linking. It is further proposed that differences in the Ig repertoire make it highly likely that fetal/neonatal, but not adult derived B cells will be induced to express CD5. The model offers a plausible explanation for the correlation of CD5 expression and natural autoantibody production by neonatal B cells. Possible sources of pathogenic autoantibody are discussed in the context of this model.

Changes in expression of J11d on murine B cells during activation and generation of memory

J11d is an antigen expressed on a variety of hemopoietic cells including B cells. In this report we describe the expression of J11d on functional subpopulations of B cells from adult mice of different ages or at different stages of an immune response. In addition we explore the relationship between the expression of J11d and that of other markers characteristic of memory B cells. Our results show that expression of J11d on B cells is related to the immunologic history of the host. Thus, J11d on B cells from normal mice is decreased as the mice age and are thereby exposed to environmental antigens. Down-regulation of J11d on B cells does not occur in germfree or nude mice but does occur when nude mice are reconstituted with T cells and/or are immunized. Since B cells expressing low levels of J11d accumulate following exposure to antigens, we also determined whether memory cells reside in the J11dlo cell population. To this end, we studied primed mice and found that expression of J11d on antigen-specific B cells increased during the first week after immunization and decreased thereafter. Increases in expression of J11d after activation also occurred in B cells stimulated with lipopolysaccharide (LPS) in vitro. However, antigen-specific B cells from long-term primed mice which expressed lower levels of J11d and antigen-specific receptors of higher affinity also expressed lower densities of sIgM and included most sIgG+ cells. Furthermore, these antigen-specific J11dlo B cells transferred a memory response, whereas J11dhi cells did not. Taken together, these data indicate that the level of expression of J11d on B cells distinguishes virgin (J11dhi) from memory (J11dlo) cells in mice.

Maternal autoimmune disease influences self-tolerance in offspring: the role of suppressor cells and materno-foetal cell traffic

Autoimmune haemolytic anaemia (AIHA) was induced in normal strain (CBA/Ca/T6) mice by repeated intraperitoneal injection of rat red blood cells (RRBC). Antibody production to cross-reactive antigens on mouse red blood cells (MRBC) and foreign antigens on RRBC was measured by the direct antiglobulin test (DGAT) and serum haemagglutination, respectively. RRBC primed female or male mice and sheep red blood cell (SRBC) primed controls were mated with naive partners and their progeny immunized with RRBC in adult life. The offspring of mothers but not fathers with active autoimmune disease showed a significant reduction in antibody response to self (MRBC) antigens, whereas the response to non-self (RRBC) was unaffected. Transfer of 30 X 10(6) spleen cells from the progeny of RRBC primed mothers into non-irradiated normal recipients resulted in selective suppression of the anti-self response following challenge with RRBC, provided that the cell donors had been boosted with RRBC 7-10 days before the transfer was performed. Thus the progeny of mothers with AIHA possessed self-reactive memory suppressor cells (Ts) shown previously to belong to the Thy-1+ I-J+ Ly-2+ T cell subset in this model. To test whether the Ts were of maternal or foetal origin the suppressor assay was repeated with spleen cells from the F1 offspring of RRBC primed B10.A(3R) (I-Jb) mothers and normal CBA(I-Jk) fathers. Pretreatment with anti-I-Jb serum plus complement completely abrogated suppression on adoptive transfer but anti-I-Jk serum failed to do so, indicating that the Ts were derived from the mothers. These findings emphasize the potential importance of Ts in induction of self tolerance during early ontogeny.

Role of dextran-specific suppressor T cells in the regulation of the immune response by a reactive form of dextran

Reactive forms of antigens or haptens have been shown to induce a state of hyporesponsiveness mediated in part by suppressor T cells. Injection of Balb/c x C57B16 F1 (CB6F1) mice with a reactive form of dextran B1355S (periodate oxidized dextran, dex-P) specifically reduced responses to dextran immunization within 1 day after dex-P treatment. This unresponsiveness lasted at least 23 days and required a reactive form of dextran for its induction since native dextran and oxidized/reduced dextran failed to induce tolerance. Furthermore, hyporesponsiveness could be induced by iv injection of dextran-coupled cells, especially peripheral blood lymphocytes, a result which suggests that in vivo coupling to cellular antigens is involved in dex-P-induced hyporesponsiveness. Suppression of the anti-dextran response could be transferred to normal mice with T-cell-enriched spleen cell populations from dex-P-injected mice. Interestingly, the presence of B cells in the transferred cell preparations interfered with detection of suppression. Both Lyt 1+2- and Lyt 1-2+ cells were involved in the dex-P-induced suppression; indeed, mixtures of these types of T cells led to the most profound degree of suppression. The suppressive activity of spleen cells from dex-P-injected mice could be removed by passage over dextran-coated plates. Moreover, cells eluted from the plates specifically suppressed anti-dextran responses of normal mice, indicating that dex-P injection induces a population of antigen-binding suppressor cells. This system will allow the study of the suppressor-T-cell receptors in a well-defined idiotypic system.

Clonal analysis of primary B cells responsive to the pathogenic bacterium Salmonella typhimurium

In the present study, a modification of the splenic focus system is used to analyze the S. typhimurium strain TML (TML)-specific B cell repertoire. The results show that the frequency of primary TML-specific splenic B cells in CBA/Ca mice is approximately 1 per 10(5) B cells and less than 30% of these B cells are specific for LPS. In contrast, the frequency of memory TML-specific cells is approximately 1 per 5-8 X 10(3) splenic B cells and greater than 95% of these B cells are specific for LPS. These results suggest that the frequency of primary TML-specific B cells is extremely low and that it expands 15-20-fold after antigen exposure. It is interesting that less than 30% of the primary B cells are specific for the LPS molecule since it is considered to be the major antigenic determinant on Salmonella organisms. Furthermore, the majority of the LPS-specific anti-TML antibody-producing clones are directed against the LPS O antigen region. Conversely, more than half to two-thirds of the memory LPS-specific anti-TML B cell clones are directed against the KDO or lipid A region of the LPS molecule. These results indicate that the preferential expansion of LPS-specific B cell clones observed after immunization resides primarily in the B cell subsets responsive to the KDO/lipid A moieties on the LPS molecule. Finally, unlike B cell responses to chemically defined antigens, TML stimulates very little IgG1 antibody. IgG2 and IgA isotypes appear to play a predominant role in anti-TML antibody responses, although all H chain classes are produced to some extent. Collectively, these findings are consistent with the responses reported for two other natural antigens, HA and PC. Hence, the pattern of stimulation by infectious agents, such as S. typhimurium, appears to be distinct from that of synthetic antigens. Thus, the studies presented herein have begun to provide insights into those subsets of B cells responsive to S. typhimurium and other infectious disease organisms.

Long-term humoral unresponsiveness in vivo, induced by treatment with monoclonal antibody against L3T4

mAbs directed against the L3T4 molecule administered in vivo caused a severe and long lasting helper cell depletion in mice. Regeneration of the L3T4+ subpopulation occurred gradually (2-3 mo) after a single antibody treatment. Experiments were designed to examine the humoral immunocompetence of such anti-L3T4-treated animals during and after regeneration of the L3T4+ T cell subset. The animals were injected with anti-L3T4, immunized with soluble antigen, and challenged with antigen every 2 wk. Antibody responses to two antigens, sperm whale myoglobin (SpWMb) and KLH, which differ with regard to their immunogenicity, were compared. The lack of humoral immune responsiveness to either of these two antigens shorty after anti-L3T4 treatment responsiveness to either of these two antigens shortly after anti-L3T4 treatment was probably due to clonal depletion. The anti-L3T4-induced immunosuppressive effect on antibody production seemed to be determined in part by the preexisting T cell repertoire, as was suggested by the recovery of responsiveness to the highly immunogenic antigen KLH and the transient inhibitory effect of anti-L3T4 treatment in primed animals. The regenerating L3T4+ T cell subpopulation was relatively incompetent in initiating B cell responses. More than 40% of the L3T4+ T cell compartment had to recover to provide help for the production of anti-KLH antibodies, whereas elimination of 90% of the L3T4+ helper cells did not inhibit a primary anti-KLH response. Evidence for a heterogeneous composition of the L3T4+ subset came from experiments using rIL-2 in vivo. The addition of rIL-2 during early helper cell depletion improved the recovery of the humoral responsiveness without apparently affecting the kinetics of the regeneration of L3T4+ T cells. Interestingly, humoral unresponsiveness to the weakly immunogenic antigen SpWMb persisted for at least 120 d. This long lasting unresponsiveness could not be explained by clonal depletion, and suggested as one possibility that the presence of antigen during regeneration of the L3T4+ helper cell population may have influenced the ultimate T cell repertoire.

Cellular basis for neonatally induced T-suppressor activity. Primary B cell maturation is blocked by suppressor-helper interactions restricted by loci on chromosome 12

The cellular mechanism and genetic restriction of neonatally induced HA-specific suppressor T (Ts) cells have been examined. The in vivo effect of these Ts cells on antibody production, primary B cell proliferation, B cell surface marker changes, and helper T (Th) cell priming during primary responses to HA have been determined. The results indicate that, although antigen-induced B cell proliferative responses and surface marker changes occur in the presence of Ts cells, differentiation to Ig secretion, and long-lived memory B cell production are prevented. Further, antigen-specific Th cell priming is completely ablated by Ts cells, suggesting that Ts act by preventing the delivery of Th signals required for both the later stages of primary B cell maturation, and the formation of memory B cell populations. Finally, in vivo cell mixing experiments using congenic mice indicate that this Ts-Th interaction is restricted by loci on mouse chromosome 12.

Hematopoietic subpopulations express cross-reactive, lineage-specific molecules detected by monoclonal antibody

The molecular specificity of a rat anti-mouse monoclonal antibody for cell surface antigens expressed by T- and B-lymphocyte subsets, erythrocytes and polymorphonuclear neutrophils (PMN) was determined. The antibody reacts with B-lymphocyte-associated molecules which migrated as a sharp 48,000 mol. wt band on SDS-PAGE. The antibody reacts with heterogeneous thymocyte and PMN molecules with a predominant mol. wt of 52,000. The same antibody reacts with heat-stable, amphipathic, organic-solvent-soluble erythrocyte molecules of mol. wt 35,000-40,000 present in Folch upper-phase ganglioside fractions, and evidence is presented that the determinant is protein-defined. Thus, a single monoclonal reagent which recognizes distinct, lineage-specific cell surface proteins on erythroid, lymphoid and myeloid elements may be used to probe not only the characteristic patterns of development of these hematopoietic subsets, but also the biochemical functions of the protein antigens themselves. In the case of B- and T-lymphocytes, such functions may extend to involvement in ligand-induced maturation and repertoire selection.

B cell repertoire diversification precedes immunoglobulin receptor expression

68 monoclonal antibodies specific for the hemagglutinin (HA) of the influenza virus, PR8, were obtained from sIg- bone marrow B cell precursors stimulated in splenic fragment cultures. Reactivity pattern (RP) analysis demonstrated that these anti-HA antibody responses included at least 29 distinguishable clonotypes. Comparison of the specificities of anti-HA antibodies obtained from sIg- bone marrow cells with those obtained from adult spleen cells indicates that the anti-HA repertoires of the two populations are comparable in diversity. Since the sIg- bone marrow B cell precursor pool presumably has not encountered V region-specific regulatory mechanisms in vivo, our data suggest that substantial diversification of the B cell repertoire precedes surface immunoglobulin (sIg) expression and subsequent interaction with environmental regulatory processes.