VASTA, G.R.*; AHMED, H.; QUESENBERRY, M.S.; ODOM, E.; O’LEARY, N.: Lectins in Protochordates and Teleost Fish: Structure-Function Relationships in Innate Immunity.

The evolutionary position occupied by the protochordates, bridging invertebrates and vertebrates, suggests that these organisms may express extant examples of the most advanced defense mechanisms that preceded the advent of immunoglobulins. A diverse lectin repertoire is present in plasma and hemocytes of the colonial tunicate C. picta. A homodimeric fucose-binding C-type lectin (CPL-III) exhibits two tandem carbohydrate recognition domains (CRDs) per 32 kDa polypeptide subunit, with structural homology to the mammalian selectins and mannose-binding lectins. Thus, CPL-III may be endowed with the ability to recognize both “self” (tunic sulfated glycan) and “non-self” (potential microbial pathogens) substances in each polypeptide subunit. The identification in C. picta of homologs of the key molecular partners in the lectin-mediated complement activation pathway described in mammals, such as components of the complement system (C3 and MASP) and hemocyte-associated galectins, suggest that this pathway is present in protochordates. Our results support the hypothesis that the lectin-mediated pathway for complement activation may have preceded the immunoglobulin-mediated pathway. The search for homologous fucose-binding C-type lectin in liver and plasma of teleost fish resulted in the identification of a novel lectin family (Supported by Grant MCB-94-06649 from the National Science Foundation)