Relaxin immunoactivaity concentrations in the peripheral sera been measured during pregnancy and parturition in rats with a homologous rat relaxin RIA. Relaxin was not detected until day 10 of pregnancy (day 10). Relaxin levels increased markedly over the next 4 days and generally ranged between 50-100 ng/ml from days 14-20. A prepartum surge in relaxin levels, which appeared to be associated with the photoperiod, occurred on day 21 in unanesthetized rats bled via indwelling jugular cannulas. Mean relaxin levels in these animals increased sharply from less than 80 ng/ml on day 20 to approximately 140 ng/ml at 1400 h on day 21 and declined to less than 60 ng/ml during the 12-24 h preceding parturition. The prepartum surge in relaxin immunoactivity may be associated with luteolysis, since there was an accelerated decline in progesterone concentrations concurrent with the prepartum relaxin surg. Rats also experienced a surge in relaxin concentrations during parturition. The mean maximal level of relaxin during parturition was approximately 180 ng/ml. The rate of decline of rat relaxin immunoactivity levels after bilateral ovariectomy on day 21 demonstrated characteristics of a multiexponential curve. The mean clearance t 1/2 from 0-30 min was 22 +/- 3 min (+/- SEM), and the mean t 1/2 from 30-180 min was 56 +/- 7 min (+/0 SEM).

Two monoclonal antibodies designated BAT085 and G3-136 were raised by immunizing BALB/c mice with gp120 purified from human immunodeficiency virus type 1 (HIV-1) IIIB-infected H9 cell extracts. Among three HIV-1 laboratory isolates (IIIB, MN, and RF), BAT085 neutralized only IIIB infection of CEM-SS cells, whereas G3-136 neutralized both IIIB and RF. These antibodies also neutralized a few primary HIV-1 isolates in the infection of activated human peripheral blood mononuclear cells. In indirect immunofluorescence assays, BAT085 bound to H9 cells infected with IIIB or MN, while G3-136 bound to H9 cells infected with IIIB or RF, but not MN. Using sequence-overlapping synthetic peptides of HIV-1 IIIB gp120, the binding site of BAT085 and G3-136 was mapped to a peptidic segment in the V2 region (amino acid residues 169 to 183). The binding of these antibodies to immobilized gp120 was not inhibited by the antibodies directed to the principal neutralization determinant in the V3 region or to the CD4-binding domain of gp120. In a competition enzyme-linked immunosorbent assay, soluble CD4 inhibited G3-136 but not BAT085 from binding to gp120. Deglycosylation of gp120 by endo-beta-N-acetylglucosaminidase H or reduction of gp120 by dithiothreitol diminished its reactivity with G3-136 but not with BAT085. These results indicate that the V2 region of gp120 contains multiple neutralization determinants recognized by antibodies in both a conformation-dependent and -independent manner.

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A panel of seven monoclonal antibodies against the relatively conserved CD4-binding domain on human immunodeficiency virus type 1 (HIV-1) gpl20 was generated by immunizing mice with purified gpl20. These monoclonal antibodies reacted specifically with gpl20 in an enzyme-linked immunosorbent assay and Western blots (immunoblots). By using synthetic peptides as antigens in the immunosorbent assay, the epitopes of these seven monoclonal antibodies were mapped to amino acid residues 423 to 437 of gpl20. Further studies with radioimmunoprecipitation assays showed that they cross-reacted with both gpl20 and gpl60 of diverse HIV-1 isolates (HTLV-IIIB, HTLV-IIIRF, HTLV-IIIAL, and HTLV-IIIWMJ). They also bound specifically to H9 cells infected with HTLV-IIIB, HTLV-IIIRF, HTLV-IIIAL, HTLV-IIIZ84, and HTLV-IIIZ34 in indirect immunofluorescence studies. In addition, they blocked effectively the binding of HIV-1 to CD4+ C8166 cells. Despite the similarity of these properties, the monoclonal antibodies differed in neutralizing activity against HTLV-IIIB, HTLV-IIIRF, and HTLV-IIIAL, as demonstrated in both syncytium-forming assays and infectivity assays. Our findings suggest that these group-specific monoclonal antibodies to the putative CD4-binding domain on gpl20 are potential candidates for development of therapeutic agents against acquired immunodeficiency disease syndrome. * Corresponding author. MATERIALS AND METHODS MAb production. The envelope glycoprotein, gpl20, of HTLV-IIIB was prepared from extracts of HTLV-IIIBinfected H9 extracts. HTLV-IIIB-infected H9 cells were lysed with a lysing buffer consisting of 10 mM Tris hydro-3579

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