Anti-Ia antibody in the sera of normal subjects after in vivo antigenic stimulation.

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Abstract
Sera from normal human subjects after antigenic challenge with intradermal PPD [purified protein derivative] or Candida antigens or with s.c. tetanus vaccine contain a factor that blocks the binding of mouse monoclonal anti-Ia antibody to Ia-positive T cells or to human Burkitt''s lymphoma B35 M cells, an Ia-positive human B cell line. The blocking activity appears 48-72 h after antigenic challenge and is gone by day 7. The appearance of the anti-Ia blocking activity coincided with a drop in the percentage of Ia-positive T cells and non-T cells in the peripheral blood of these subjects and with a decrease in the density of surface Ia on the non-T cell population. The blocking was not genetically restricted: serum from a given subject blocked anti-Ia binding to Ia-positive T cells of subjects with different HLA-DR haplotypes. The blocking activity was contained in the IgM fraction of the sera. The blocking activity of the sera was eliminated after absorption of the sera with Ia-positive but not with Ia-negative human cell lines. The blocking of monoclonal anti-Ia binding may be caused by an IgM anti-Ia antibody that appears in normals after in vivo antigenic challenge.

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