Interaction of mannose-binding lectin with HIV type 1 is sufficient for virus opsonization but not neutralization

Mannose-binding lectin (MBL), a microbe-recognition protein in serum, binds to high mannose glycans on HIV-1 gp120 and has been reported to neutralize the cell line-adapted strain HIV(IIIB). Because HIV primary isolates (PI) are generally more resistant to neutralization by antibodies and considering that PI are produced in primary cells that could alter the number of high mannose glycans on HIV relative to cell lines, we assessed the ability to MBL to neutralize HIV PI. MBL at concentrations up to 50 microg/ml mediated relatively little neutralization (<20%) of HIV PI infection of peripheral blood mononuclear cells (PBMCs). MBL-neutralizing activity was slightly higher for cell line-adapted HIV infection of the H9 T cell line (up to 64% at 50 microg/ml). However, this effect was specific for H9 cells since MBL did not neutralize cell line-adapted virus infection of PBMCs, HIV PI infection of the GHOST cell line, or VSV pseudotyped with HIV gp160 from cell line-derived virus or PI. In contrast to its low activity in neutralization assays, MBL efficiently bound infectious HIV PI and opsonized HIV PI for uptake by monocytic cells. These results show that both PI and cell line-adapted HIV, despite binding of MBL, are relatively resistant to neutralization by levels of MBL normally present in serum. However, binding and opsonization of HIV by MBL may alter virus trafficking and viral-antigen presentation during HIV infection.