Human immunodeficiency virus (HIV) strains can be separated into two types: HIV and HIV-related West African viruses. Site-directed serology using synthetic peptides offers possibilities for the determination of type-specific antibodies. A 22-amino-acid peptide with the sequence Ala-Ile-Glu-Lys-Tyr-Leu-Glu-Asp-Gln-Ala-Gln-Leu-Asn-Ala-Trp-Cys-Ala-Phe-Arg-Gln - Val-Cys representing a conserved region of the transmembranous protein of simian T-cell lymphotropic virus-type III (STLV-III; related to West African HIV) was used as antigen in an enzyme-linked immunosorbent assay (ELISA). In parallel, tests were performed with a pair of previously described peptides, including the homologous region of the glycoprotein (gp) 41 of the HIV strain HTLV-IIIB. In tests with three groups of 20 sera it was shown that the different peptide ELISAs allowed a categorical distinction of antibodies to the two types of HIV. Tests using peptide antigens may provide excellent opportunities for large-scale testing for type-specific antibodies against HIV. The tests are simple, sensitive and specific and are readily standardized.
Two partially overlapping 19 and 22 amino acids long peptides representing a highly immunogenic site of the transmembranous glycoprotein (gp41) of human immunodeficiency virus (HIV) were used as antigen in ELISA tests. The results of antibody determination with this assay were compared with those of three or more conventional ELISAs and Western blot (WB) tests and radioimmunoprecipitation assay. Twenty-six sera from patients with AIDS or LAS and from asymptomatic carriers of HIV infection all showed a pronounced reaction in the peptide ELISA as well as positive results with other tests. In contrast, 27 sera from laboratory workers and blood donors were negative by all tests. A group of 39 blood donor sera, which had shown false positive or ambiguous results in the ELISAs and sometimes in WB tests employed for confirmation, also were negative in all cases with the peptide ELISA. Consecutive samples collected from individuals with primary HIV infection were also analyzed. In 6 out of 9 cases, the peptide ELISA revealed an antibody response within one month after onset of clinical symptoms and sensitivity for antibody detection equaled that of other ELISA tests. Eight sera from five West African persons infected with HIV-related viruses did not react in the peptide ELISA, reflecting differences in properties of the envelope components. The peptide ELISA used in this study appears to represent a simple technique employing chemically synthesized antigen for accurate and sensitive estimation of antibodies to the HIV group of nontransforming human retroviruses.
The IgG subclass distribution to the E34/E32 peptides, derived from the HIV-1 glycoprotein 41 transmembrane protein, was analyzed in ELISA. Sera from individuals at different stages of the disease were assayed. A restricted subclass response of mainly IgG1 and IgG2 was found. The subclass response was of a different type than the one observed to HIV whole Ag and to a synthetic peptide from the C'-terminal part of the HIV-1 p24 core protein. An increased subclass restriction was observed in progressed stages of the disease.
In a previous report, it was shown that spleen cells from mice made tolerant to human γ-globulin (HGG)5 could specifically inhibit the immune response of normal spleen cells after adoptive transfer to lethally irradiated recipients. However, that report also showed that the suppressive activity was only transiently associated with tolerant spleen cell populations. It was concluded from those experiments that while suppressive activity could be demonstrated in tolerant spleen cells under certain conditions, such activity was not obligatory for the maintenance of the tolerant state. The experiments presented here were performed to determine the nature of the effector cell(s) and the target cell(s) involved in this system of suppression of the immune response. Treatment of cells from tolerant animals with anti-thymocyte serum and complement to remove thymus-derived (T) cells completely abrogated suppressive activity. Removal of adherent cells from tolerant spleen cells by passage over glass wool columns resulted in partial loss of the suppression. The inhibitory activity of the suppressor cells was resistant to 900 R irradiation regardless of whether the tolerant spleen cells were irradiated before or after adoptive transfer. The cellular target(s) for the suppressor cells was examined by using lipopolysaccharide (LPS) as an alternative source of helper activity for the response to HGG. LPS, injected at the time of the initial antigenic challenge of mice that had been reconstituted with tolerant and normal spleen cells, prevented the expression of suppression against bone marrow-derived (B) cells. However, when LPS was presented only at the time of the secondary antigenic challenge, it was unable to overcome suppression of the immune response of reconstituted recipients. Thus, LPS could produce a state where the B cells were resistant to suppression, but LPS could not rescue the responsiveness of B cells once the cells in the reconstituted recipient had been suppressed. In addition, the immune responses to both the hapten dinitrophenol (DNP) and the carrier (HGG) were suppressed when recipients of tolerant and normal spleen cells were challenged with DNP 6HGG. This indicates that T helper cells are also a target for suppression. The results presented in this paper are discussed in relation to a possible mechanism of suppression which proposes that suppressive activity represents the induction of tolerance in immunologically competent cells by HGG which is closely associated with the tolerant spleen cells.
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