Evidence that blocking factors in the sera of multiparous mice are associated with immunoglobulins

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Abstract
Previous work has shown that lymph-node cells from pregnant BALB/c mice can kill syngeneic tumor cells in a microcytotoxicity assay, and that sera from pregnant BALB/c mice can block (inhibit) that effect. The present study shows that passage of such sera through immunoadsorbents charged with anti-mouse IgG2a or IgG2b removed the blocking activity, and that this could be recovered in the eluates; passage through an anti-IgG1 immunoadsorbent was less effective in decreasing blocking serum activity and adsorption to immunoadsorbent charged with anti-IgM or anti-IgA did not remove it at all. Passage of blocking serum through an immunoadsorbent coupled with antibodies from a rabbit anti-mouse embryo antiserum removed all of its blocking activity, and this could be recovered in the eluates. The findings are compatible with the hypothesis that the blocking factors operating in this system are largely complexes between embryonic antigens and IgG2a and IgG2b.