IgG subclass, IgE, and IgA anti-trinitrophenyl antibody production within trinitrophenyl-Ficoll-responsive B cell clones. Evidence in support of three distinct switching pathways.

Abstract

The IgM, IgG subclass, IgE and IgA anti-trinitrophenyl (TNP) antibody (Ab) response of B cells to the type 2 antigen TNP-Ficoll was studied in athymic nude mice and in the in vitro splenic focus assay. Results from the splenic focus assay in which purified B lymphocyte preparations had been transferred to irradiated nu/nu recipients indicate that many TNP-Ficoll stimulated B cell clones secrete multiple isotypes and, hence, appear to be undergoing intraclonal isotype switching. Although the frequency of clones secreting each of the IgG subclasses correlated with 5'' to 3'' Igh-.gamma. gene order, the frequency of IgE- and IgA-secreting clones did not appear to be influenced by the respective position of Igh-.epsilon. and Igh-.alpha. on the chromosome. Unlike clones that secreted anti-TNP Ab of the IgG subclasses, IgE and IgA anti-TNP Ab-secreting clones did not have a high propensity for coexpression of isotypes encoded by 5'' Igh-C genes. Three distinct switching pathways may be employed by B cells responding to TNP-Ficoll: a common IgG pathway, an IgE pathway and an IgA pathway. The presence of T cells resulted in a preferential enhancement of the production of anti-TNP Ab of those IgG subclasses which were least represented in the absence of T cells, i.e., IgG2b and IgG2a. No significant enhancement of IgE anti-TNP clonal frequency was found in the presence of T lymphocytes, but T cells significantly enhanced the clonal expression of IgA anti-TNP Ab. Although a relatively large number of B cell clones synthesized IgE and IgA anti-TNP Ab in the splenic focus assay, relatively little or no secretion of these isotypes was detected in immune mice. Possible explanations for this apparent discrepancy are discussed.