A reappraisal of "T-independent" antigens. II. Studies on single, hapten-specific B cells from neonatal CBA/H or CBA/N mice fail to support classification into TI-1 and TI-2 categories.

Spleen cells from adult CBA/H or CBA/N mice, or from neonatal CBA/H mice, were fractionated on thin layers of fluorescein (FLU)-gelatin to yield FLU-specific B lymphocytes. A single cell, or small numbers ranging from 1 to 10, were cultured in 10-microliter microcultures together with various antigens and mitogens. The results were compared with those of bulk culture or limiting dilution cultures supported by thymus filler cells. B cell growth and differentiation-promoting conditioned media (BGDA) were added to some cultures. The CBA/N results gave no support to the commonly used classification of T cell-independent (TI) antigens into TI-1 and TI-2 categories. A typical supposed TI-1 antigen, FLU-LPS, strongly stimulated normal adult single FLU-specific B cells to proliferate and form antibody, but virtually failed to trigger CBA/N B cells of comparable antigen-binding avidity. The same was true of LPS or LPS plus dextran sulfate acting as mitogens. The allegedly TI-2 antigen FLU-Ficoll, although still triggering comparatively poor responses, was actually marginally more active than FLU-LPS. FLU-Brucella abortus (FLU-BA) + BGDA gave the best results with single CBA/N B cells, but still induced only 1.27% of cells to develop into antibody-forming clones vs 12.2% with CBA/H cells. The results obtained with single neonatal B cells also lent no support to the distinction between TI-1 and TI-2. Both "TI-1" and "TI-2" stimuli caused adequate proliferation, one "TI-2" antigen stimulating 23.2% of the cells. None of the antigens caused good antibody formation, however, probably because multivalent antigens can deliver signals impeding the differentiation of immature B cells. It is therefore suggested that the classification of TI-1 antigens into two subcategories be abandoned, at least for the time being.