Could neutralization activity be removed by adsorption to U87-CD4-CCR5 cells?

FC serum was incubated with intact U87-CD4-CCR5 cells, and the recovered serum was then tested for PI virus neutralization.

Figure 7: Pooled FC vaccine serum was incubated with U87-CD4-CCR5 cells (white squares) or in an empty microculture well (mock;black squares). Pooled FI serum (COS-env + U87-CD4) was similarly treated (white and black circles, respectively). Sera were tested for remaining neutralizaton of 168P with U87-CD4-CCR5 cells.

Was FC serum neutralization reduced when observed on adsorption to U87-CD4-CCR5 cells? Answer No reduction in FC serum neutralization was observed.

Conclusion? That FC serum neutralization targets highly conserved envelope protein structures that arise transiently during binding and fusion.

But, is it still possible to have situations in which unidentified antibodies to the cell could be contributing to the antiviral effect?

A possible situation: neo-antigens might be induced on the U87-CD4-CCR5 cell surface during the hours over which fusion occurs, perhaps in consequence of the assault on membrane integrity that cell-cell fusion represents. Antibodies to such epitopes could have an adverse effect on target cells during neutralization assays; they would not necessarily be removed during the absorption experiments, or produced during the immunizations with control, nonfusing cells.

A possible situation: The effective antibodies in the immune sera are actually directed against altered conformations of the CD4 and CCR5 receptors and not against the viral envelope glycoproteins.

A possible solution? If and when larger animals, such as macaques, are used, more answers will be found. The greater yield of immune serum from these more relevant animals should allow identification of the particular antigens that are recognized by the effective antibodies.

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