Interaction of mannose-binding lectin with primary isolates of human immunodeficiency virus type 1

Mannose-binding lectin (MBL) is present in human serum and plays an important role in innate immunity by binding to carbohydrate on micro-organisms. Whereas the gp120/gp41 of human immunodeficiency virus type 1 (HIV-1) contains numerous N-linked glycosylation sites and many of these sites contain high-mannose glycans which could interact with MEL, the interaction between MBL and primary isolates (PI) of HIV-1 has not been studied. To determine if PI of HIV bind to MEL, a virus capture assay was developed in which virus was incubated in MEL-coated microtitre wells followed by detection of bound virus with an ELISA for p24 antigen. The X4 HIV-1(MN) T cell line-adapted strain and PI of HIV (R5 and X4) bound to MEL. Binding of virus to MEL was via the carbohydrate-recognition domain of MBL since binding did not occur in the absence of Ca2+ and was blocked by preincubation of MEL-coated wells with soluble mannan. The interaction of virus with MEL-coated wells was also inhibited by preincubation of virus with soluble MEL, indicating that both immobilized and soluble forms of MEL bound to HIV, Although host cell glycoproteins are incorporated into the membrane of HIV, binding of virus to immobilized MEL required expression of gp120/gp41 on virus particles, suggesting the presence of either an unusually high carbohydrate density and/or a unique carbohydrate structure on gp120/gp41 that is the target of MEL. This study shows that PI of HIV bind to MEL and suggests that MEL can selectively interact with HIV in vivo via carbohydrate structures on gp120/gp41.