The mechanism of antigenic competition. I. The macrophage as a site of a reversible block of T-B lymphocyte collaboration

Intestinal immunoregulation: lessons from human mendelian diseases

The mechanisms that maintain intestinal homeostasis despite constant exposure of the gut surface to multiple environmental antigens and to billions of microbes have been scrutinized over the past 20 years with the goals to gain basic knowledge, but also to elucidate the pathogenesis of inflammatory bowel diseases (IBD) and to identify therapeutic targets for these severe diseases. Considerable insight has been obtained from studies based on gene inactivation in mice as well as from genome wide screens for genetic variants predisposing to human IBD. These studies are, however, not sufficient to delineate which pathways play key nonredundant role in the human intestinal barrier and to hierarchize their respective contribution. Here, we intend to illustrate how such insight can be derived from the study of human Mendelian diseases, in which severe intestinal pathology results from single gene defects that impair epithelial and or hematopoietic immune cell functions. We suggest that these diseases offer the unique opportunity to study in depth the pathogenic mechanisms leading to perturbation of intestinal homeostasis in humans. Furthermore, molecular dissection of monogenic intestinal diseases highlights key pathways that might be druggable and therapeutically targeted in common forms of IBD.

Translating molecular insights in autoimmunity into effective therapy

Autoimmunity and the pathogenesis of autoimmune diseases were a major focus of the Walter and Eliza Hall Institute, where I started my research career. After my initial studies on immune cell culture and immune regulation, I returned to an analysis of the pathogenesis of human autoimmunity in London. Linking upregulated antigen presentation to autoimmunity led to an investigation of the role of cytokines in rheumatoid arthritis (RA), in collaboration with Ravinder Maini. These experiments defined the concept of a TNF-dependent cytokine cascade driving the manifestations of RA, which led to successful clinical trials of anti-TNF monoclonal antibody in RA patients, heralding a major change in medical practice. This success was made possible by enthusiastic support from many laboratory and clinical colleagues and taught us that cytokines are important rate-limiting steps and hence good therapeutic targets. My current scientific challenge is exploring the hypothesis of whether all major medical needs can be approached via cytokine blockade.

Specificity and in vitro transfer of the immunosuppressive effect of detergent-disrupted influenza virus vaccine

Primed murine splenocytes give an in vitro antibody response to influenza whole virus vaccine (WVV), as measured by enzyme immunoassay (EIA). When subunit vaccine (SV) of either influenza A or influenza B virus was added to in vitro splenocyte cultures stimulated with WVV, the EIA antibody response to homologous WVV was reduced. This reduction in antibody response was observed when SV was prepared using zwitterionic detergent (empigen BB), non-ionic detergent (triton-X-100) or cationic detergent cetyl-trimethyl ammonium bromide (CTAB); it was found to be effected only by SV of strains of the same virus subtype--when SVs prepared from a heterotypic (H3N2) strain, an H1N1 strain and an influenza B strain were added to splenocyte cultures in the presence of WVV. When splenocytes from immunologically naive mice, exposed in vitro to SV, were transferred to secondary cultures of primed splenocytes, the antibody response to WVV in the secondary cultures was also reduced. Mechanisms that may suppress the in vitro antibody response are discussed.

Antigen specific T cell factors

Antigen specific helper and suppressor factors have a similar structure, with two major sections, a 'variable region', determining antigen specificity which is likely to be controlled by Immunoglobulin VH genes, with which it shares idiotype and framework determinants. Specific factors also have a 'constant region' which does not vary between strains and minimally between species or with the antigenic specificity of the factors, which are defined by rabbit anti-helper or anti-suppressor antisera. This region determines the biological function of the molecule. Anti-Ia antisera react with factors, but the nature and function of Ia molecules on T cell factors is still unclear. The model of specific factor structure, with C and V regions resembles that of immunoglobulin, and it is thus possible that the C region of factors, like the V region is Ig linked. Because there are multiple T cells, helping and suppressing antibody responses specifically, it seems improbable that all of these cells could interact directly with rare antigen-specific B cells. Thus we propose that macrophage presenting cells are the key to the integration of signals for immune induction and regulation for T and B cells. Since Ir genes have been identified in the macrophage presenting cells interacting with both T and B cells, this suggests that macrophage Ia antigens are of importance in the integration of triggering signals for the lymphoid pool.

Comparison of antigen-specific I-region-associated cell interaction factors

Two basic types of factors reacting with anti-I region (anti-Ia) antisera are compared, those derived from macrophage-like antigen presenting cells and others derived from T-lymphocytes, of either the suppressor or helper type. Despite the common property of reacting with anti-Ia antisera, the two sets of factors differ by many criteria. Macrophages, upon culture with antigen, release complexes of Ia antigen and a fragment of the original immunogen. This material is only produced by responder macrophages and thus appears to be a soluble Ir gene product. The genetic restriction of the T-macrophage interaction was investigated in chimeras, and it was found that the host environment as well as the donor genotype was of importance in determining restrictions, which were thus not really directed to "self." There was no evidence for intrinsic T-cell Ir genes, as nonresponder stem cells developed into responder T-cells in a (responder X nonresponder) F1 environment. However, these cells only responded in the presence of responder macrophages. Specific T-cell factors are different in nature. These all react with anti-Ia antisera, but the nature or function of the T-cell Ia is unknown. The basic structure involves a VARIAble region" responsible for antigen binding which, as it reacts with anti-idiotype antisera and anti-variable region framework antisera is an immunoglobulin variable region. There is also a "constant region," defined by its biological properties as well as by specific rabbit antisera. This two-region nature of specific factors is reminiscent of immunoglobulin structure and it is a reasonable hypothesis that the constant region is linked to the Ig cluster of genes.

Reversal of immunosuppression induced by murine leukemia viruses

BALB/c mice infected with Rowson-Parr virus, a lymphatic leukemia virus isolated from the Friend complex, undergo a rapid depression of antibody response. Spleen cells from these mice in culture show a similar deficit in the response to stimulation with sheep red cells and inhibit the reactivity of normal splenocytes. In an attempt to reverse this immunosuppression, near normal responses were obtained in vitro from infected splenocytes by increasing antigen dose, by adding E. coli lipopolysaccharide, or, more effectively, by cocultivating with small numbers of unfractionated or T cell-depleted peritoneal exudate cells (PC), whereas other manipulations proved ineffective. PC did not prevent the inhibition of normal splenocytes by infected spleen cells, but exhibited substantial restorative activity in vivo. In similar experiments, the immunosuppression exerted by the entire Friend complex could be reversed by PC in vitro but not in vivo. These results indicate that a functional deficit of macrophages may be partially responsible for the immunological impairment induced by leukemia viruses and suggest rational approaches to evaluate the relevance of this impairment to oncogenesis.

Immunological effects of IgT synthesized by theta-positive cell lines

The effects of immunoglobulin (Ig) purified by affinity chromatography from two cultured T cell lines on in vitro immune responses was studied. IgT purified from both EL-4 and WEHI-22 suppressed the thymus-dependent IgM response, but had no effect on the thymus-independent IgM response. In contrast, the IgG responses to both thymus-dependent and independent antigens were augmented at optimal concentrations of IgT. Ig of B cell origin--serum Ig, myeloma Ig, B cell surface Ig -- did not have any of these effects. Because of the similarity of the effects of IgT purified from the lymphomas with the effects of T cells and their IgT, it seems likely that the IgT obtained from EL-4 and WEHI-22 cell lines are analogues of normal IgT and thus should be useful in elucidating some of the chemical and biological properties of IgT.

Immune response gene (Ir-SRBC) exerts its effect via macrophages in inbred rats

In the previous report, strain differences of inbred rats were investigated in the antibody response to sheep erythrocytes (SRBC). A low-responder strain (Fischer rats) produced only IgM antibody, but other high-responder strains switched over from IgM to IgG antibody to SRBC. Pretreatment with incomplete Freund's adjuvant made Fischer rats a high-responder. These results seemed to indicate that there are malfunctions of macrophages, together with T cells, in Fischer rat strain. In this report, strain differences in the phagocytic activity of macrophages were examined using radiolabelled SRBC. High uptake of SRBC by the spleen in the low responder rats, and vice versa, was confirmed in various experimental conditions. Genetic analyses were made of the specific spleen uptake of the radiolabelled SRBC in backcrossed rats. The result clearly showed that the degree of spleen uptake of the radiolabelled SRBC is genetically determined by a single gene and this property itself has a close negative correlation with the ability of each rat to produce haemolysin against SRBC. These results strongly suggest that the Ir-SRBC gene exerts its effect, at least in part, via macrophages. The relationship between the function of the macrophage and the antibody response is discussed.