Brief De6ni6ve Report

We have recently demonstrated that monocytes and K lymphocytes can decrease the viability of group C meningococci (Mgc) in cooperation with human sera from persons immunized with group C meningococcal polysaccharide (Csss) (I). This antibody-dependent ceU-mediated (ADC) antibacterial mechanism occurs in the absence of added complement (1) as does antibody-dependent cellular cytotoxicity (ADCC) by K lymphocytes and monocytes against eucaryotic target cells (2). IgA isolated from patients convalescing from meningococcal disease, by virtue of its inability to fix complement, blocks IgGand IgM-dependent complement-mediated killing of Mgc (3, 4). The experiments in this paper were designed to test if this convalescent IgA, known to be immunologically free of and functionally different from IgG and IgM, could induce monocyte-mediated anti-meningococcal activity. The purity and functional integrity of the IgA used is particularly important because previous studies in which the opsonic activity of IgA was tested, have yielded conflicting results (5-9).