Comparison of antibodies directed against human respiratory syncytial virus antigens present in two commercial preparations of human immunoglobulins with different neutralizing activities.

Antibodies directed against human respiratory syncytial virus (HRSV) from two commercial preparations of human immunoglobulins (Igs) were compared. One of the Ig preparations (RespiGam) was obtained from blood samples selected for high titres of anti-HRSV neutralizing antibodies. The other preparation (Flebogamma) was obtained from unselected blood donations. RespiGam and Flebogamma had very similar anti-HRSV ELISA titres, but RespiGam neutralized virus infectivity 8-10 times more efficiently than Flebogamma. The same behaviour was observed when purified antibodies from RespiGam and Flebogamma, specific for either the fusion (F) or the attachment (G) glycoprotein, were compared. To gain further information about differences in neutralization between these two Ig preparations, antibodies recognizing certain F and G protein fragments or peptides were purified and their neutralizing activities were compared. In general, antibodies purified from RespiGam showed higher neutralizing activity that those purified from Flebogamma, but those differences were higher with antibodies specific for certain protein segments than for others. Some of the protein regions recognized by human neutralizing antibodies were mapped outside antigenic sites identified previously with panels of murine monoclonal antibodies. These results offer the possibility of searching for new neutralizing antibodies that could be used to study the molecular basis of neutralization and to prevent HRSV infections.