An alpha2-macroglobulin associated factor produced by T lymphocytes which provides polyclonal stimulation of B lymphocytes to maintain the turnover of their surface Ig.
The supernatant of 'crowded' but not 'spread' rabbit spleen cell cultures contains a macroglobulin factor which behaves in an Ig-turnover assay as any T-independent antigen or polyclonal B-cell activator (PBA). In the supernatants of crowded rabbit lymphoid cell cultures prepared in serum free medium, the factor was found to be associated entirely with the alpha-macroglobulin (alpha M) fraction (alpha 1 + alpha 2). This alpha M was most probably actively secreted by the lymphocytes because: (i) sequential supernatants obtained in serum free medium of crowded cultures contained equal amounts of alpha M as well as equal PBA activity; (ii) the alpha M became labelled when the cells were grown in medium containing a radioactive amino acid. Macrophages were not required for the production of PBA. PBA was not produced when either crowded B or T cells were cultured alone but only when they were cultured together. Purified T cells were not triggered by any plant lectin to produce PBA. By use of anti-alpha 2M allotype antibodies and B and T cells from different rabbits, the PBA was shown to have the allotype of the T-cell donor. The PBA was associated with rabbit alpha 2M but not alpha 1M. We concluded that upon close contact, B cells stimulate T cells to produce a PBA associated with alpha 2M.
D000818:Animals; D001402:B-Lymphocytes / Q000276:immunology; D002478:Cells, Cultured; D007375:Interleukin-1; D011506:Proteins / Q000276:immunology*; D011817:Rabbits; D011863:Radioimmunoassay; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism*; D012397:Rosette Formation; D013601:T-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D000511:alpha-Macroglobulins / Q000096:biosynthesis / Q000276:immunology*
D007375:Interleukin-1; D011506:Proteins; D011947:Receptors, Antigen, B-Cell; D000511:alpha-Macroglobulins