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We have been studying which portions of mouse IgG2b and IgG2a immunoglobulins are recognized by their specific Fc receptors on mouse macrophages by using CNBr fragments. One fragment from the C H 2 domain of IgG2b binds uniquely to the γ2b Fc receptor while the γ2a Fc receptor binds two fragments, widely spaced, one from the C H 2 domain and one from the C H 3 domain. In both a rosetting assay and a radioactive binding assay, fragments H-5 and H-10 compete with intact IgG2a protein for binding to the γ2a Fc receptors. In addition, the binding of H-10 appears to augment the binding of the H-5 fragment. These data suggest that 1) a sequence in the C H 2 domain is sufficient for binding to the γ2b Fc receptor, 2) sequences of two domains are important in the binding of IgG2a to its Fc receptor on mouse macrophages and 3) the binding of a sequence from the C H 3 domain may induce a conformational change in the receptor such that binding to a sequence in the C H 2 domain is increased or stabilized.

Kohler and Milstein (1975) launched a new era in immunological research by showing that somatic cell hybridization could be used to generate a continuous “hybridoma” cell line producing a monoclonal antibody. The hybridoma technology has already fulfilled one of the major goals that immunologists have been trying to achieve for years: the routine production of large amounts of homogeneous antibody against a wide variety of antigens. Each of the subsequent chapters in this monograph will illustrate the usefulness of such reagents.

Sera of 27 members of 3 human kindreds with familial systemic lupus erythematosus (SLE) were examined for expression of a cross-reactive idiotype present on anti-DNA antibodies of SLE patients. By radioimmunoassay, serum samples from 6 of 8 SLE patients and 15 of 19 family members had high-titered reactivity with the antiidiotype, 3I. Isoelectric focusing and Western blot analysis of 3I-reactive bands revealed two patterns of reactivity: either a pattern of bands present at pH 5-7, or bands present at pH 5-7 with additional bands present at pH 7-8.5. Cationic bands were found to correlate with the presence of anti-DNA antibodies, indicating that immunoglobulin charge may be a factor in determining specificity for DNA. Millipore filter analysis revealed anti-DNA antibodies in sera of 4 of 8 SLE patients and 2 of 19 family members without SLE. In 2 additional SLE patients and 2 additional family members, anti-DNA antibodies were revealed when sera were analyzed under conditions that dissociate immune complexes. This study indicates that expression of an idiotype associated with anti-DNA antibodies is significantly increased in relatives of SLE patients and usually occurs in the absence of anti-DNA activity.

Antinative DNA antibodies were purified from the serum of a patient with active systemic lupus erythematosus. Using hybridoma technology, we produced several mouse monoclonal antibodies directed against idiotypic determinants on these antinative DNA antibodies. One of these monoclonal anti-idiotypic antibodies, 3I, an IgG2a Kappa, was extensively characterized. 3I is believed to be directed against an idiotypic determinant because (i) its reactivity with antinative DNA antibodies is not inhibited by a large excess of pooled human serum, (ii) it reacts with F(ab')2 fragments of antinative DNA antibodies, and (iii) it reacts with antinative DNA antibodies of all IgG subclasses. 3I is not directed against the antigen binding site in that native DNA and 3I do not compete for binding to antinative DNA antibodies. Eight of nine sera containing antinative DNA activity as determined by the Millipore filter assay reacted with 3I in a solid-phase radioimmunoassay. These findings suggest that antinative DNA antibodies from nonrelated patients with systemic lupus erythematosus share a common idiotype.

Entry of blood-borne pathogens into the spleen elicits a series of changes in cellular architecture that culminates in the systemic release of protective antibodies. Despite an abundance of work that has characterized these processes, the regulatory mechanisms that coordinate cell trafficking and antibody production are still poorly understood. Here, marginal zone (MZ) B cells responding to streptococcus in the blood were observed to migrate along splenic nerves, arriving at the red pulp venous sinuses where they become antibody-secreting cells. Electrical stimulation of the vagus nerve, which in turn regulates the splenic nerve, arrested B-cell migration and decreased antibody secretion. Thus, neural circuits regulate the first wave of antibody production following B-cell exposure to blood-borne antigen.