PHAGOCYTIC PERIPHERAL-BLOOD MONOCYTES FROM RABBITS AND HUMANS EXPRESS MEMBRANE-RECEPTORS SPECIFIC FOR IGM MOLECULES - EVIDENCE THAT INCUBATION WITH NEURAMINIDASE EXPOSES CRYPTIC IGM (FC) RECEPTORS

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  • 1 January 1979
    • journal article
    • research article
    • Vol. 35  (3) , 484-490
Abstract
Phagocytic human and rabbit peripheral blood monocytes, identified by their ingestion of polystyrene particles, were investigated for the presence of surface membrane receptors for Ig[immunoglobulin]M molecules. After incubation of freshly isolated monocytes with IgM anti-sheep erythrocyte (SRBC) preparations, a mean of 0.7% of human monocytes and a mean of 16.2% of rabbit monocytes formed rosettes with SRBC. If the monocytes were pre-incubated with Vibrio cholerae neuraminidase (VCN), these figures increased to 32.6% and 37.8%, respectively. The specificity of rosette formation by VCN-treated monocytes was established in several experiments. SRBC sensitized with a F(ab'')2 preparation of an IgG anti-SRBC reagent completely failed to rosette with VCN-treated monocytes, and inclusion of IgM, but not other Ig or non-Ig protein molecules in the test medium, inhibited rosette formation. Most importantly, rosette formation by human monocytes was inhibited by F(c)5.mu. but not by Fab.mu. fragments. Rabbit and human monocytes apparently express IgM-class specific membrane receptors for IgM molecules and these receptors may be cryptic or hidden but can be revealed by treatment with VCN. The human monocyte IgM receptor is F(c) specific. The rabbit monocyte IgM receptor was trypsin-resistant.