Dan Holmberg

From an Antigen‐Centered, Clonal Perspective of Immune Responses to an Organism‐Centered, Network Perspective of Autonomous Activity in a Self‐Referential Immune System

O que vemos, não e’o que vemos, senão o que somos1

A “Trans” Perspective on the Control of Immunoglobulin C Gene Expression

The control of immunoglobulin (Ig) C gene expression is, for molecular biologists, a question DNA recombination or RNA processing, while for immunologists it is the class specificity in the antibody responses to structurally different antigens. For cell biologists, it might be a problem of regulating membrane-associated versus secretory forms of a protein, or growth versus maturation in clonal progenies. It is, overall, a question of cell differentiation, and for allofusitprovidesa very simple system-eight genes of known structure and eight products easily identifiable yet one that is most attractive, as it may offer one of the first model systems in biology in which DNA recombination is directly induced by well-defined signals. In addition, it also appears to be one of the areas in basic immunobiology closest to providing direct application of fundamental principles to clinical practice.

Idiotypic multireactivity of 'natural' antibodies. 'Natural' anti-idiotypes also inhibit helper cells with cross-reactive clonotypes.

One hundred and twenty IgM‐secreting hybridomas derived from unmanipulated 6‐day‐old BALB/c mice were screened for reactivity with the prototype idiotypic and anti‐idiotypic monoclonal antibodies, defining three well established systems, namely TEPC 15:10/13–15, J558:CD3.2, and MOPC 460:F6(51). Up to 25% of all IgM antibodies reacted with at least one of the six specific ligands, half of the latter being ‘monospecific’, the others reacting with two or more aniibodies. A detailed analysis of the four most multi‐reactive clones showed individually specific patterns of reactivity and revealed reactions of the same IgM molecule in idiotypic systems previously studied independently. Furthermore, when tested for functional interactions with syngeneic helper T cells expressing MOPC 460‐like clonotypes, one of these antibodies was found to inhibit effector helper activity. The results show the existence of ‘natural antibodies’ with idiotypic reactivities related to recurrent clonotypes in the strain. They may be either ‘specific’ or ‘mullireactive’, and might connect idiotypes on T and B cells and on antigenic systems so far studied independently.

IgM-Induced Specific Antibody Responses: Direct Correlation between Responsiveness and Natural or Induced Recurrence of the Idiotype

The idiotype (Id) expressed on antibodies of the trinitrophenol (TNP)‐spccific BALB/c hybridoma TNP.11 is defined as a ‘nonrecurrent’ or private Id in BALB/c mice, whereas the analysis of splenic plaque‐forming cells (PFC) and circulating antibody in DBA/2 mice immunized with TNP antigens revealed that TNP.11 is a ‘recurrent’ Id in this strain. TNP.11 antibodies were characterized by their ability to induce an antigen‐independent anti‐TNP response in these two strains. Whereas this antibody was negative in BALB/c mice [18], a clearcut increase in splenic anti‐TNP PFC, preferentially expressing the TNP.11 Id, was observed in DBA/2 mice. This correlation between Id recurrency and ability to induce antigen‐independent responses was further probed in BALB/c mice repeatedly immunized with anti‐TNP.11 Id antibodies (Ab3). Such BALB/c mice express the TNP.11 Id in detactable amounts even without antigen challenge and respond with increased numbers of splenic anti‐TNP PFC to the injection of low amounts of TNP.11 antibody. These findings suggest that the ability of an antibody to induce antigen‐independent PFC responses is associated with the‘recurrency’, either natural or induced, of the antibody Id.

Idiotypic characterization of antibody-induced antibody responses

Anti-idiotypic antisera were produced in syngeneic (C57BL/6) mice against a monoclonal anti-Dextran B512 (Dex) antibody (38-13). In radioimmunoassays, anti-idiotypic antibodies were shown to react with the homologous idiotype, while failing to recognize another monoclonal anti-Dex antibody, independently derived from C57BL/6 mice (D-16). Plaque inhibition tests confirmed the specificity of the anti-idiotypic antibodies and revealed that the 38-13 idiotype is expressed by about half of all anti-Dex antibodies produced in C57BL/6, but not in CBA mice. Injection of normal (but not athymic) C57BL/6 mice with low doses of 38-13 monoclonal antibodies, contained culture supernatants or ascitic fluids, resulted in a 10-20 fold increase in the numbers of anti-Dex PFC detected in the spleen 5 days later, the majority of which carried the 38-13 idiotype.

The Immune Response to Bacterial Dextrans.: I. Genetic Control of Responsiveness

The in vivo antibody response to the thymus‐independent (TI) antigen dextran B512 (Dex) was studied in various mouse strains. We found no non‐responder strains but rather that the magnitude of Dex‐specific plaque‐forming cell and serum antibody responses varied markedly among individual mice, even if these were of the same age and litter and kept in the same environment. This was the case both for mouse strains previously described genetically as high (IgCHb, j) and for those described as low (IgCHa) responders to Dcx [14]. In‘low’‐responder BALB/c mice, the responsiveness to Dex increased with age, such that a large fraction of these mice responded as well as‘high’‐responder C57BL/6 mice. Analysis of aged back‐cross populations derived from IgCHb and IgCHa parental strains further substantiated these findings. Thus, all backcross mice, irrespective of IgCH haplotype. responded on the average equally well to Dex. According to our studies, therefore, the assignation of high or low responsiveness to IgCH locus‐linked genes cannot be done unequivocally.

Internal Activity of the Immune System and its Physiologie Significance

After the introduction of Jerne’s network theory 10 years ago, modern views of the immune system have been strongly influenced by the ideas of autonomy previously developed by those working on complex systems such as the brain. This “new immunology” attempts to describe the normal immune system as it is, the fundamental characteristics of its Organization and, in the words of Francisco Varela, “the landscape of its eigen behaviours.” Within this perspective, the study of the internal activity of the immune system, of the generation and decay of its cellular and molecular components, is likely to provide more relevant information as to the physiology of immune activity than the study of immune responses to the injection of large doses of antigen, as in classical approaches.