In the present study we have investigated whether bovine erythrocytes (Eb) specifically sensitized with human polyclonal IgA1 (Eb-IgA1) are able to bind to resident adherent rat peritoneal cells (PM phi). Rat PM phi formed rosettes with Eb-IgA1 at room temperature and at 37 degrees. The formation of these rosettes could be blocked completely by excess human serum IgA or myeloma IgA1. In contrast, human IgG or rat IgG did not inhibit the formation of rosettes, whereas human polymeric myeloma IgA2 only partially inhibited rosette formation. Complete inhibition of rosette formation was also induced by rat monomeric and polymeric myeloma IgA, suggesting species interchangeability. Furthermore, rosette formation could be completely blocked in the presence of excess asialofetuin or D-galactose, while excess ovalbumin or D-mannose had no effect. These results suggest that the oligosaccharides in the hinge region of human IgA1 are involved in the binding of Eb-IgA1 to rat PM phi.