MECHANISMS OF ANTIINFLUENZA ACTIVITY OF SURFACTANT PROTEIN-A AND PROTEIN-D - COMPARISON WITH SERUM COLLECTINS

The present study provides the first direct comparison of anti-influen za A virus (IAV) activities of the collectins surfactant protein (SP) A and SP-D, mannose-binding lectin (MEL), and conglutinin. SP-D, MEL, and conglutinin inhibited IAV hemagglutination activity with a greater potency than and by a distinct mechanism from SP-A. Although isolated trimeric SP-D carbohydrate recognition domains inhibited hemagglutina tion activity, preparations of SP-D also containing the collagen domai n and NH2 terminus caused greater inhibition. In contrast to SP-A (or nonmultimerized SP-D), absence of the N-linked attachment did not effe ct interactions of multimerized SP-D with IAV. SP-D, SP-A, and conglut inin caused viral precipitation through formation of massive viral agg regates, whereas MBL formed aggregates of smaller size that did not pr ecipitate. All of the collectins enhanced IAV binding to neutrophils; however, in the case of MBL, this effect was modest compared with the binding enhancement induced by SP-D or conglutinin. These studies clar ify the structural requirements for viral inhibition by SP-D and revea l significant differences in the mechanisms of anti-IAV activity among the collectins.