Dirofilaria immitis: Surface properties of third- and fourth-stage larvae

Abstract

The objective of this study was to analyze surface properties of larval Dirofilaria immitis with potential relevance to protective immunity. Comparisons were made between third (L 3)- and fourth-stage larvae (L 4) based on their net surface charge, surface carbohydrate and antigen composition, ability to nonspecifically absorb host proteins, complement activation, and nonspecific cellular adherence. It was determined that L 3 had a net negative surface charge, whereas L 4 had either a neutral or weakly positive surface charge. The lectin Con A, but not any of the other lectins tested, bound only to the surface of L 4, and not to that of L 3. Monoclonal antibodies were prepared which reacted with the surface of L 3 or with the surface of L 4, but never both. L 4 were found to nonspecifically adsorb host protein to their surfaces, whereas L 3 did not. Both L 3 and L 4 were found to activate complement through the alternate pathway. Finally, nonspecific cellular adherence was found on L 3 both in vitro and in vivo but not on L 4. The surfaces of L 3 and L 4 were thus shown to be significantly different and, potentially, in ways which would have great impact in the generation and effectiveness of a protective immune response.