Abstract
The primary in vitro IgM response to the major histocompatibility (MHC) antigens expressed on chicken red blood cells (CRBC) has been shown to critically depend on the cooperation between antigen-specific helper factor from CRBC-primed thymus-derived helper (T) cells, bone marrow-derived (B) cells, and radioresistant (A) cells. A 500- to 1000-fold enrichment for immunocompetent B cells by means of a rosette technique permitted the culturing of as few as 2000 B cells that yielded on the average 500 plaque-forming cells against CRBC within 3 days of culture. Cell reconstitution experiments clearly showed that the presence of A cells can be circumvented by an A cell-derived secretory product. This is in disagreement with the hypothesis that helper factor acts as a mediator for antigen presentation on the A cell surface membrane. The spectrum of helper factor cross-reactivity with respect to certain alleles of the B locus was found comparable to that of antibody.
