Contained indirect viable-cell membrane immunofluorescence microassay for surface antigen analysis of cells infected with hazardous viruses

Human immunodeficiency virus infection elicits early antibody not detected by standard tests: implications for diagnostics and viral immunology

The FDA-approved tests for diagnosis of HIV exposure depend on detection of specific antibody in serum. HIV infection is missed in some individuals because they score seronegative by the standard clinical EIA and Western blot assays. This apparent immunological "silent" period following infection may last for months and has been reported to be as long as 3 years in rare cases. Is there truly a lack of an immune response or is there a more subtle, narrowly focused antibody response in these HIV-infected individuals which is not detected by the current tests? Using a nondenaturing serological assay (immunofluorescence of live infected T-cells), we found that each of four infected individuals "seronegative" by the standard tests did possess antibody against native HIV proteins expressed on infected cells. These antibodies reacting with native HIV antigenic epitopes were of the IgG isotype, they cross-reacted with many, but not all, of seven random HIV-1 isolates, and one of the sera immunoprecipitated HIV gp160 from NP-40-solubilized infected cells. These results show that seronegative, high-risk, infected individuals can actually be seropositive and that different types of assays using native antigenic epitopes may be required for screening. Implementation of these findings thus may decrease HIV transmission. These results also highlight the importance of protein conformation for many natural viral antigenic epitopes.

Heterogeneity of human immunodeficiency virus cell-associated antigens and demonstration of virus type specificities of human antibody responses

We examined the antigens of human immunodeficiency viruses (HIV) expressed on infected H9 cells using live-cell membrane immunofluorescence and immunofluorescence absorption. Application of this nondenaturing serological method permitted analysis of HIV antigenic determinants maintained in their native configurations on the cell surface. Sera from infected individuals were found to react variably with H9 cells productively infected with nine different HIV isolates, and certain sera were completely unreactive with some isolates. Absorption of the sera prior to use in immunofluorescence revealed extensive heterogeneity of HIV cell-surface antigens and multiple type-specific antibodies in patients' sera. Immunoprecipitation and SDS-PAGE analysis of radiolabeled cell-surface proteins indicated that the predominant serological reactions were to env-encoded proteins. The observed antigenic and antibody heterogeneity likely reflects env sequence heterogeneity which has been previously reported for different HIV isolates. The demonstration of antigenic diversity among HIVs and the importance of defining the native antigenic epitopes, particularly those most widely shared, are important issues that must be considered in vaccine development.

Characterization of target cells for MCF viruses in AKR mice

The recombinant (MCF) class of murine leukemia virus appears to play an important role in lymphomagenesis in AKR and other mice. Although much effort has been extended in characterizing MCF viruses, relatively little is known about the cells they infect. I examined what cells were targets in AKR mice for both lymphomagenic and nonlymphomagenic MCF viruses. Lymphomagenic MCF viruses of thymic origin (AKR-247 and C58L1) were found to infect and replicate selectively in immature lymphocytes only present in thymic cortex, whereas nonlymphomagenic MCF viruses of splenic origin (C58v-1-C77 and C58v-2-C45) selectively infected and replicated in cells that appeared to B lymphocytes. Virus-binding studies suggested that neither T- nor B-lymphocyte tropisms were determined by selective attachment of virus to the respective cells. These findings demonstrate that in contrast with ecotropic viruses, which can infect many types of cells in the mouse, specific cellular tropisms can exist for MCF viruses, and that MCF infection, and therefore oncogenicity, is closely linked to cellular differentiation.

MCF-specific murine monoclonal antibodies made against AKR-247 MCF virus recognize a unique determinant associated with the gp70-p-15(E) complex

Hybridomas obtained from (NFS X AKR)F mice immunized with syngeneic cells infected with AKR-247 MCF virus produced antibodies specific for only AKR-247 or closely related MCF viruses which hare a previously defined MCF antigen (MCFA-3). These monoclonal antibodies recognized a new type of viral antigenic determinant which appeared to be a conformational determinant associated with the env precursor polyprotein (pr80env) or its disulfide-linked gp70-p15(E) complex (gp80) but not with free gp70 or p15(E) or any other virion or virus-induced protein.

Genetic study of lymphoma induction by AKR mink cell focus-inducing virus in AKR x NFS crosses

The mink cell focus-inducing (MCF)-247 virus, originally isolated from an AKR thymoma, is lymphomagenic in AKR mice but not in the ecotropic virus-negative NFS mouse strain. Analysis of sensitivity to lymphoma-induction by AKR-247 MCF virus in genetic hybrids between these two strains showed that F1 mice inoculated as sucklings were uniformly sensitive, whereas those inoculated as weanlings were generally resistant. In NFS backcross mice inoculated as sucklings, inheritance and expression of endogenous ecotropic virus from AKR was an essential correlate of replication of MCF virus and subsequent development of lymphoma. However, one-third of the mice expressing ecotropic virus and replicating the inoculated MCF virus did not develop lymphoma. The results suggested that an additional gene that influenced development of lymphoma may be involved, and that mice inheriting both virus-inducing loci from AKR were more susceptible than those inheriting only one. These findings indicate that the causal role of ecotropic virus infection in spontaneous thymomagenesis in AKR mice involves not only the generation of leukemogenic MCF viruses but also the establishment of permissiveness for their growth.

Cell-surface antigens associated with recombinant mink cell focus-inducing murine leukemia viruses

Distinct type-specific antigens were detected on cells infected with cloned mink cell focus-inducing (MCF) murine leukemia viruses by means of cell surface immunofluorescence absorption assays with rabbit antisera raised against naturally-occurring AKR MCF viruses. The MCF type-specific antibodies were present in high titer and not absorbable by cells infected with ecotropic, xenotropic, or wild mouse amphotropic murine leukemia viruses, or combinations of ecotropic and xenotropic viruses. Three MCF subtype-specific reactions were identified. One subspecificity (operationally designated MCFA-1) defined antigenic determinant(s) distributed among MCF viruses in general. Another (MCFA-2) specified determinant(s) induced by all naturally occurring MCF isolates not of Friend or Moloney origin. A third subspecificity (MCFA-3) was induced by some MCF isolates, and not by others; the presence of this antigen did not correlate with the source of any presently known biological property of the viruses. In addition, type-specific antigenic determinants of ecotropic and xenotropic murine leukemia viruses were expressed on MCF virus-infected cells. The serological profile of MCF viruses thus supports the contention that they are env gene recombinants between ecotropic and xenotropic murine leukemia viruses. However, new, distinct MCF-specific determinants are also generated, and these could be useful markers in studying MCF viruses.