| Abstract: | The capacity of membrane immunoglobulin A (IgA)-bearing B cells to respond to specific antigen in the absence of T cell influences has not been defined. A human-human hybridoma, constructed from an Epstein-Barr virus transformed tonsil B cell that secreted IgA anti-phosphorycholine (PC) and a human plasmacytoma cell, was utilized to examine this issue. The cloned hybridoma expressed membrane IgA and secreted IgA specific for PC. Stimulation of the hybridoma cells with PC conjugated to Sepharose beads (PC-Sepharose) but not glycine-conjugated Sepharose resulted in an increase in DNA synthesis. Affinity purified goat anti-human IgA bound to Sepharose also augmented DNA synthesis. Soluble PC did not increase DNA synthesis and inhibited the increase in DNA synthesis resulting from PC-Sepharose. IgA secretion was augmented in response to PC-Sepharose, as demonstrated by an increase in the number of Ig-secreting cells detected by a reverse hemolytic plaque assay and by quantitation of the IgA secreted per cell by enzyme-linked immunosorbent assay. Mitogen-stimulated T cell supernatants increased IgA secretion of the hybridoma cells but did not cause synergistic stimulation of the cells in the presence of PC-Sepharose. These data indicate that Sepharose-bound antigen was sufficient to induce proliferation and augment IgA secretion by this membrane IgA anti-PC-bearing hybridoma. The results suggest that cross-linking of membrane IgA by specific antigen may be a sufficient stimulus for proliferation and differentiation of B cells at this stage of maturation. |
