NATURAL IGM ANTIBODIES IN BABY RABBIT SERUM BIND HIGH-MANNOSE GLYCANSON HIV TYPE-1 GLYCOPROTEIN-120 160 AND ACTIVATE CLASSIC COMPLEMENT PATHWAY/

Serum from rodents and felines has been found very effective in comple ment-dependent lysis of HIV-1, even in nonimmunized animals, but the e ffector molecules in animal serum and target structures on HIV-1 envel ope gp120/160 responsible for complement activation were not determine d. We have found that the natural anti-carbohydrate-specific IgM antib odies present in baby rabbit serum were able to lyse effectively the C D4(+) T cells coated with the whole virus or with a recombinant gp120/ 160, irrespectively of the virus strain ar glycoprotein expression sys tem, When the high mannose-type glycans on gp160 were enzymatically re moved by endoglycosidase F or blocked with the specific lectins, the c omplement activation and subsequent cell lysis were abolished. IBM-dep leted baby rabbit serum was not able to lyse the gp120/160- and/or who le virus-coated target cells. These results suggest that the target st ructures for complement-activating and naturally occurring IgM antibod ies in baby rabbit serum are high-mannose residues on HIV-1 envelope g lycoprotein.