Antigen-initiated B-lymphocyte differentiation. VII. Quantification of AFC progenitor levels in adoptive and culture responses to NIP-POL antigen.

Quantitative studies on B cells require a direct assay for antibody-forming cell (AFC) progenitor function, in which the number of AFC produced bears a simple, linear arithmetic relationship to the number of progenitors present. This might be expected under conditions where helper T-cell and accessory cell requirements are by-passed, or provided in excess. This possibility has been tested using as antigen the hapten NIP (4-hydroxy-3-iodo-5-nitrophenylacetic acid) on the carrier POL (polymerized bacterial flagellin), in adoptive transfer of normal and nude mouse spleen cells to irradiated recipients, and in cell culture. Primary and secondary IgM responses to this antigen are "T cell-independent'. The secondard IgG response is T cell-dependent but this function can be provided by 'carrier-primed' irradiated recipients. However in no case did the cell dose response curve show a linear, arithmetic relationship between cells transferred or cultured, and AFC produced. If less than 10 X 10(6) cells were adoptively transferred or cultured, a sigmoid curve was obtained, approximately linear with a slope of around 1-6 on a log-log scale. In adoptive transfer, a plateau was then seen above 10 X 10(6) cells, followed by a second sharp rise beginning around 15 X 10(6) cells. Addition of irradiated spleen cells as 'fillers' to maintain cell numbers constant produced a linear (arithmetic scale) dose response curve for the primary IgM responses, both adoptive and in culture. Lipopolysaccharide injection of recipients also produced linear regions in the adoptive transfer system. These techniques provide more direct, quantitative assay systems for the primary IgM responses to this antigen. However, arithmetic linear cell dose response curves were still not obtained for the secondary IgG responses, using irradiated filler cells.