AGGREGATION AND OPSONIZATION OF TYPE-A BUT NOT TYPE-B HAEMOPHILUS-INFLUENZAE BY SURFACTANT PROTEIN-A

The ability of surfactant protein A (SP-A) to aggregate and opsonize t ype a and b Hemophilus influenzae was investigated. Type a, but not ty pe b, was aggregated by SP-A. Aggregation was maximal at 24 mug SP-A/m l and was Ca2+-dependent. Aggregation of type a was inhibited by D-glu cosyl-BSA but not by high concentrations of monosaccharides (D-mannose , D-galactose, D-glucose, or L-fucose) or by sialic acid, purified typ e a capsular polysaccharide, or type IV collagen. In Western blots, I- 125-labeled SP-A bound to the major outer membrane protein (putatively P2) of type a hemophilus by a Ca2+-dependent mechanism. This binding was competitively inhibited by excess unlabeled SP-A. I-125-labeled SP -A also bound to the major membrane protein of type b, but at less tha n 5% of the level observed for type a. SP-A did not bind to lipooligos accharides of either type a or type b. SP-A increased association of t ype a, but not type b, hemophilus with alveolar macrophages. After ops onization with SP-A, type a hemophilus were killed by alveolar macroph ages, as indicated by bactericidal assays and the release of soluble, radiolabeled products from leukocytes. It is concluded that SP-A aggre gated and opsonized type a hemophilus, but not type b, possibly becaus e SP-A bound to the P2 outer membrane protein of type a to a greater e xtent.