Idiotypic characterization of antibody-induced antibody responses

Extensive splenic B cell activation in IgM-transgenic mice

Two lines of IgM-transgenic mice were analyzed for the state of activation of their splenic compartment, with regard to the frequency of large cells in the different lymphoid subpopulations, and to the isotype distribution of background plasma cells. We observed an extensive B cell activation preferentially involving B lymphocytes co-expressing transgenic and endogenous IgM (IgD), and resulting in massive immunoglobulin class switch. Nearly all splenic plasma cells contain endogenous immunoglobulins, with frequencies of IgG and IgA plasma cells significantly higher than in normal mice. There are virtually no plasma cells that produce only the transgenic IgM. Moreover, only a proportion of plasma cells producing endogenous immunoglobulins co-express the transgenic product. In addition to these observations that apply to both transgenic lines, differences were found between the two lines concerning the quantitative expression of the transgenic IgM, the frequency of cells expressing the transgene and the magnitude of switch. These data are indicative of the complexity of the IgM-transgenic mouse model, in which the phenomenology may depend on the transgene insertional position, on B cell physiology and on immunological mechanisms of recognition, induction and regulation.

The immune response to bacterial dextrans. VI. No correlation between the frequency of cells expressing a major anti-dextran idiotype and the idiotype profiles of specific antibody responses

C57BL/6 mice respond to Dextran B512 (Dex) with a predominant idiotype (Id) (17-9) while no such Id-positive antibodies are identified in the specific antibody response of BALB/c mice. We used limiting dilution systems to determine the absolute frequencies of clonal B-cell precursors producing the 17-9 Id in these two mouse strains and analysed the correlation between Id-expression and antibody activity at the clonal level. The results show very similar frequencies of anti-Dex and Id-positive B cells in both strains, but C57BL/6 mice contained fourfold higher frequencies of Dex-specific clonal precursors which are Id-positive. This kind of clone, although not used in the specific response of BALB/c mice, constitute roughly 20% of their anti-Dex repertoire and they are readily induced in this strain. Thus, immunization of both strains with anti-idiotypic antibodies results in the production of Id-positive anti-Dex antibodies with serum titres that directly correlate with precursor frequencies. The results show, therefore, that the section of clonal repertoires utilized in a primary immune response varies with the immunogen, even if thymus-independent. These observations are discussed in the context of the genetic controls of anti-Dex antibody responses and on the general question of the utilization of available antibody repertoires in immune responses.

On the validity of using lipopolysaccharide-driven limiting dilution systems for clonable B-cells to analyse functional antibody repertoires

Analyses of B-cell repertoires by mitogen-driven limiting dilution systems (LDA) followed by specific antibody detection on immobilized antigens (ELISA), while constituting the only method available to determine absolute frequencies of any given specificity, provide no indications as to the functional ability of clonal precursors scored as positive to actually respond to antigen in vivo. We have now addressed this question by quantitating dextran alpha 1----6-specific clonal precursors among small, resting, and large activated B cells in the spleens of mice, before and after priming with optimal doses of antigen. The results demonstrate that virtually all B cells scored as antigen-specific in LDA/ELISA systems do respond to antigen and undergo blast transformation after priming in vivo.

Self versus non-self carrier in primary and secondary anti-TNP B cell response: I. Specificity of help

Humoral anti-hapten responses are supposed to require carrier-specific help. Yet, "TNP-specific" help can be activated with TNP coupled to syngeneic lymphocytes. To further clarify the role of hapten-specific vs. carrier-specific helper T cells (TH) in the humoral anti-TNP response, BALB/c mice were immunized with TNP coupled to cellular or soluble self or non-self carriers, and we analyzed primary and secondary B cell responses as well as the apparent specificity of help. TNP bound to syngeneic red blood cells (sRBC), syngeneic albumin (sA) and syngeneic polyclonal or monoclonal immunoglobulin (sIg/smIg) and TNP coupled to non-self carriers initiated equivalent primary anti-TNP responses. On the other hand, a secondary anti-TNP response was only obtained with heterologous carriers or with smIg. Even with heterologous carriers or with smIg, the magnitude of the secondary anti-TNP response exceeded only slightly the amplitudes of a primary anti-TNP response. Furthermore, if animals were challenged shortly after priming, they appeared un/-hyporesponsive. In vitro analysis revealed that in the primary as well as in the secondary anti-hapten response, TNP-specific TH were involved, i.e., the primary response to sIg, sA and sRBC was exclusively due to TNP-specific help, the response after priming with TNP-smIg or TNP-heterologous carrier was due to the additive effects of carrier- and TNP-specific help. Since "carrier-specific" help with smIg was independent of the antibody specificity as well as of the Ig class, we suppose that smIg activated idiotype-specific TH, which functioned like "carrier" TH. Two mechanisms were responsible for the low magnitude of the secondary anti-hapten response: competition for carrier-specific help (using heterologous carriers), and antibody (AB)-dependent suppression.

Purification of an IgM antibody response-enhancing factor to the alpha 1-6 epitope of native dextran from serum and supernatants from T-cell hybridomas

We have found that some hybrids produced by fusing AKR thymoma BW 5147 with spleen cells from Dx-hyperimmunized CBA mice produce factors that affect the primary CBA IgM PFC response. By the use of HPLC-DEAE chromatography, sometimes combined with affinity chromatography, we have purified from hyperimmune anti-Dx serum, from ascites-growing T hybrids, and from normal CBA serum a family of factors that specifically enhance the anti-Dx IgM response. They show specificity for either Dx or anti-Dx, they may contain an Iak determinant, and they are genetically restricted in their function. The factors from all three sources are found in the same fractions after separation and move in fractions without Ig contamination. The affinity-purified factor was eluted at an NaCl concentration of 0.15-0.20 M. On the basis of these characteristics we believe that we have separated a class of T cell-derived helper factors from serum. The concentration of the factor in serum increases after hyperimmunization with Dx. As a specificity control we show that the same sera contain a natural anti-SRBC IgM response-enhancing factor. It co-separates with the anti-Dx-enhancing factor, but they can be distinguished by their preferential binding to their own antigens.

The repertoire of anti-TNP antibodies in mice neonatally suppressed with anti-IgM

Previous studies have shown that mice immunized with TNP-Ficoll when young, adult, or aged expressed different repertoires of anti-TNP antibodies. The aim of the present study was to find out whether this age-related nonrandom progression was driven by antigen, and whether it was regulated by the immune network through surface-Ig receptors on B lymphocytes. The approach utilized was to block receptor expression on B lymphocytes of mice by the chronic administration of anti-IgM from birth for approximately 1 year, and then compare their subsequent antibody response to that of age-matched control animals. The results obtained have shown that the age-dependent shift in the anti-TNP repertoire expressed could take place in animals whose B lymphocytes were blind to antigen and anti-id for the greater part of their lives and thus suggest that the regulatory events responsible for this shift may be (surface Ig) receptor independent.

The immune response to bacterial dextrans. III. Ontogenic development and strain distribution of specific clonal precursors

The frequencies of B512 dextran (Dex)-specific B cell precursors were determined by limiting dilution analysis in a number of mouse strains originally described as "high responder", "low responder" and "nonresponder" to this antigen. No significant difference in the frequencies of Dex-specific precursors was found in C57BL/6, B10.BR, C3H/Tif, BALB/c and A/Sn adult mice. Together with the large intra-strain variability in the magnitude of anti-Dex PFC responses in vivo, these results established that differential reactivity in vivo cannot be ascribed to genetically controlled absence or wide variation in the frequency of Dex-specific immunocompetent precursors. A similar analysis of the Dex-specific precursor frequency was carried out in C57BL/6 mice between 1 week and 3 months of age. While no Dex-specific antibody response was detected in vivo before the age of 3 weeks, clonal precursor analysis revealed that the appearance of these specificities parallels the development of competent (IgM-producing) B lymphocyte clonal precursors, such that no significant difference in absolute frequencies of Dex-specific precursors could be observed among these age groups. This is interpreted to suggest that the late development of the Dex-specific antibody responses is regulatory rather than due to late rearrangement and activation of the appropriate V genes and a sequential expression of antibody specificities in ontogenic development.

From the mechanisms of lymphocyte activation to internal activity in the immune system

The principles of lymphocyte activation were summarized for all three sets of immunocompetent cells: B cells, cytotoxic cells and helper T lymphocytes. They were then used to derive the basic mechanisms and specificities which drive internal activity in the normal immune system and which select available antibody repertoires. It was postulated that "natural antibodies" are induced by "natural helper cells" and are selected on the basis of their idiotypic profiles, which are complementary to available T-helper-cell repertoires. "Natural idiotypes" would then carry idiotopes similar to MHC epitopes, the predominant germ-line specificity of T-cell repertoires.

An example of major histocompatibility complex-linked control of idiotypic interactions

Normal euthymic mice, injected i.v. with low doses of syngeneic monoclonal antibodies carrying "recurrent" idiotypes, develop a specific increase in numbers of splenic IgM plaque-forming cells that are paratopically and idiotypically similar to the injected antibody. We have now studied the responsiveness to a C57BL/6 anti-dextran a(1 leads to 6) and BALB/c anti-TNP (trinitrophenyl) monoclonal antibodies in a variety of strains. It was found that such responses are controlled by two linkage groups, namely major histocompatibility complex (MHC) and Ig-1.