The mechanism of natural binding of bacteria to human lymphocyte subpopulations.

Some bacteria bind naturally to human lymphocyte subpopulations. Here we investigated the nature of the interacting factors" on bacterial cells and on lymphocytes. First, surface Ig was not involved in the binding of B. melitensis to B cells, since capping of surface Ig did not affect the binding of this bacteria. We put forward the hypothesis that the binding is due to an interaction between a protein (probably a lectin) on the lymphocyte surface and a carbohydrate on the bacteria. The following observations were consistent with this hypothesis: (1) the binding of B. melitensis to B cells was prevented by alpha-methyl-D-mannoside (alpha-MM) but not by other sugars; (2) the binding of B. melitensis to B cells was prevented by pretreatment of the peripheral blood lymphocytes (PBL) with 257 mM of alpha-MM but pretreatment of the bacteria had no effect; (2) an Escherichia coli mutant (strain 2023) which binds to B cells and part of the T cells was also agglutinated by Concanavalin A (Con A) but the nonbinding parental strain was not; the binding of this mutant to B cells was also inhibited by 257 mM of alpha-MM; (4) bacteria that bind to human lymphocytes were agglutinated at high titers by various plant lectins while those that do not bind were not agglutinated or were agglutinated only at low titers; (5) bacteria that bind to B cells as well as those that bind to B and T cells all were agglutinated by Con A, Lens culinaris agglutinin and Pisum sativum agglutinin, whose carbohydrate specificities were alpha-D-mannosyl- and alpha-D-glucosyl-residues; (6) the "receptors" on lymphocytes but not those on bacteria were sensitive to pronase digestion; and (7) bacteria still bound after being heated at 121 degrees C or being fixed with formaldehyde. Thus, we suggest that one of the mechanisms by which bacteria bind to lymphocytes may be by the interaction between a lectin on the lymphocyte and a carbohydrate on the bacteria.