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C Susal, M Kirschfink, M Kropelin, V Daniel and G Opelz
Department of Transplantation Immunology, Institute of Immunology,
University of Heidelberg, Germany.
Recombinant glycoprotein 120 (rgp120) of human immunodeficiency virus
type-1 (HIV-1) activates the human complement system in the absence of
anti-gp120 antibodies. HIV-1 glycoprotein gp120 can dissociate from the
viral envelope either spontaneously or after binding of HIV-1 to the CD4
molecule. As a consequence, gp120 can circulate in the patient's serum and
attach to the surface of uninfected CD4+ T cells. Complement activation by
cell-bound HIV-1 glycoprotein gp120 with subsequent opsonization may
represent a mechanism for the elimination of uninfected CD4+ cells by the
reticuloendothelial system, thereby enhancing the progression of HIV
disease. In the current study, the complement proteins C4,C3,C5,C9, and
properdin were found to bind to a synthetic peptide covering positions
233-251 of the gp120BRU sequence on incubation with normal human serum.
Complement activation by the peptide was comparable with that induced by
aggregated IgG, complete rgp120, and the previously described
complement-activating gp41-peptide 609-623. Activation occurred via the
classical pathway and was abrogated in the presence of EDTA, Mg2+/EGTA, or
C4-deficient human serum. Peptides partly overlapping the sequence 233-251
activated complement to a lesser extent. The complement-activating capacity
of the gp120 sequence 233-251 was not restricted to the HIV-1BRU isolate,
because a peptide from the corresponding sequence of the HIV-1MN strain was
also capable of activating complement. An additional strong
complement-activating site was identified in the gp120 sequence 321-360 of
the HIV-1MN strain. These data indicate that distinct sites in gp120 are
able to activate human serum complement via the classical pathway in the
absence of anti-gp120 and independent of glycosylation.
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