The specificity of naturally occurring heterophile antibodies in normal rabbit serum.

Rabbit sera used as a complement source contain cytotoxic antibodies which reacted with cultured human cells. This cytotoxic activity can be inhibited by human IgM. The capacity of IgM mu and L chains, and IgM glycopeptides to inhibit these heterospecific antibodies was determined. The inhibitory activity of several monosaccharides, bacterial polysaccharides and blood group substances was also determined. At least some of the heterospecific antibodies in normal rabbit sera are directed against carbohydrate determinants. Mannose, fucose, and bacterial polysaccharides containing mannose as the immunodominant sugar are particularly effective in inhibiting cytotoxic antibodies.