J Virol. MAbs were screened for the ability to inhibit cell-cell fusion. In contrast to MAbs generated against sgp140, the seven MAbs produced by using this protocol did not react with Env SR 3576 by Western blotting and were strongly positive by FACS analysis, and several reacted preferentially with oligomeric Env. All seven MAbs potently neutralized SIVmac1A11, and several neutralized SIVsmB670 CL3 and/or SIVsm543-3E. MAbs that inhibited gp120 binding to CD4, CCR5, or both were recognized in both organizations. MAbs to the V3 loop and one MAb reactive with the V1/V2 loop interfered with CCR5 binding, indicating that these regions of Env play related functions for SIV and human being immunodeficiency virus. Amazingly, several of the MAbs generated against infected cells clogged CCR5 binding inside a V3-self-employed manner, suggesting that they may identify a region analogous to the conserved coreceptor binding site in gp120. Finally, all neutralizing MAbs clogged illness through the alternate coreceptor STRL33 much more efficiently than illness through CCR5, a finding that offers important implications for SIV neutralization assays using CCR5-bad human being T-cell lines. Human being and simian immunodeficiency viruses (HIV and SIV) are closely related retroviruses that create AIDS in humans and related immunodeficiency syndromes in some varieties of macaques, respectively. SIV illness of rhesus macaques has become an important animal model for HIV illness and AIDS in humans and for the development of an effective HIV vaccine (20). Several reports have shown the humoral immune response can, under some conditions, protect nonhuman primates from illness by HIV, SIV, or SHIVs (SIVs that are designed to consist of an HIV type 1 [HIV-1] Env protein) (28, 41, 57, 72, 79). In addition, infections by SIVs with partially deglycosylated Envs have generated neutralizing antibodies that can efficiently neutralize wild-type computer virus in vitro (73), while immunization of mice with cells expressing fusion-competent HIV-1 Env elicited humoral reactions that could neutralize several primary computer virus isolates in vitro (52). Finally, recent findings have shown the passive administration of neutralizing monoclonal antibodies (MAbs) could prevent mucosal and in utero transmission of pathogenic SHIVs (3, 58). Collectively, these findings raise hope that an appropriately designed Env-based SR 3576 immunogen will generate a protecting humoral response to HIV. A key feature of any effective vaccine against HIV will be the ability to protect against illness with multiple, divergent isolates. Regrettably, the humoral response elicited by monomeric gp120 is not broadly cross-neutralizing, making it unlikely that vaccination with this form of Env will prevent illness from the heterogeneous viruses circulating in the general populace (10, 12). HIV and SIV Env glycoprotein is definitely expressed on the surface of the virus like a noncovalently linked oligomer, and immunization with oligomeric Env preparations offers been shown to generate antibodies that preferentially identify oligomeric Env (8, 24). A correlation between antibody reactivity with oligomeric Env and neutralization ability has been noted in several reports (30, 64, 69, 76). With these studies in mind, we immunized mice with cell-associated or soluble forms of oligomeric SIV Env in an attempt to elicit broadly cross-reactive, neutralizing antibodies. A secondary goal was to create a large panel of well-characterized MAbs directed toward varied epitopes throughout SIV Env; while SR 3576 many antibodies to HIV have been explained and their binding sites have been determined, much less is known about the antigenic structure of SIV Env. As will become described, a number of MAbs reactive with the V3 or V1/V2 loops or less well-defined conformational determinants on gp120 derived from both protocols were capable of neutralizing related and more divergent isolates. Several of these MAbs have been shown to interfere with Env binding to CD4 and/or the CCR5 coreceptor. A large number of nonneutralizing MAbs with epitopes distributed throughout the Env protein have also been generated. This panel of well-characterized MAbs should be highly useful for long term structure-function and immunologic studies of SIV Env. MATERIALS AND METHODS Preparation of purified SIV Env. The CP-MAC gene (49) was cloned into pSC65, and a premature quit codon was launched just N terminal to the membrane-spanning (transmembrane [TM]) website using PCR-based mutagenesis. A recombinant vaccinia computer virus (vAE1) was made by using this plasmid and the Western Reserve vaccinia SR 3576 computer virus strain, using standard techniques (23). To HES7 generate recombinant protein, BHK cells were infected with vAE1 at a multiplicity of illness of 10. Four hours post illness, cells were washed twice with phosphate-buffered saline (PBS), and serum-free Dulbecco altered Eagle medium (DMEM; Gibco-BRL) was added. Cell supernatant was harvested 24 h postinfection, cleared by centrifugation, and filtered through a.