J. Steven McDougal

Human T-lymphotropic virus type III (HTLV-III) or lymphadenopathy-associated virus (LAV) is tropic for human T cells with the helper-inducer phenotype, as defined by reactivity with monoclonal antibodies specific for the T4 molecule. Treatment of T4+ T cells with monoclonal antibodies to T4 antigen blocks HTLV-III/LAV binding, syncytia formation, and infectivity. Thus, it has been inferred that the T4 molecule itself is a virus receptor. In the present studies, the surfaces of T4+ T cells were labeled radioactively, and then the cells were exposed to virus. After the cells were lysed, HTLV-III/LAV antibodies were found to precipitate a surface protein with a molecular weight of 58,000 (58K). By blocking and absorption experiments, this 58K protein was identified as the T4 molecule. No cell-surface structures other than the T4 molecule were involved in the antibody-antigen complex formation. Two monoclonal antibodies, each reactive with a separate epitope of the T4 molecule, were tested for their binding capacities in the presence of HTLV-III/LAV. When HTLV-III/LAV was bound to T4+ T cells, the virus blocked the binding of one of the monoclonal antibodies, T4A (OKT4A), but not of the other, T4 (OKT4). When HTLV-III/LAV was internally radiolabeled and bound to T4+ T cells which were then lysed, a viral glycoprotein of 110K (gp110) coprecipitated with the T4 molecule. The binding of gp110 to the T4 molecule may thus be a major factor in HTLV-III/LAV tropism and may prove useful in developing therapeutic or preventive measures for the acquired immune deficiency syndrome.

OBJECTIVE: To determine the range of antinuclear antibodies (ANA) in "healthy" individuals compared with that in patients with systemic lupus erythematosus (SLE), systemic sclerosis (SSc; scleroderma), Sjögren's syndrome (SS), rheumatoid arthritis (RA), or soft tissue rheumatism (STR). METHODS: Fifteen international laboratories experienced in performing tests for ANA by indirect immunofluorescence participated in analyzing coded sera from healthy individuals and from patients in the 5 different disease groups described above. Except for the stipulation that HEp-2 cells should be used as substrate, each laboratory used its own in-house methodology so that the data might be expected to reflect the output of a cross-section of worldwide ANA reference laboratories. The sera were analyzed at 4 dilutions: 1:40, 1:80, 1:160, and 1:320. RESULTS: In healthy individuals, the frequency of ANA did not differ significantly across the 4 age subgroups spanning 20-60 years of age. This putatively normal population was ANA positive in 31.7% of individuals at 1:40 serum dilution, 13.3% at 1:80, 5.0% at 1:160, and 3.3% at 1:320. In comparison with the findings among the disease groups, a low cutoff point at 1:40 serum dilution (high sensitivity, low specificity) could have diagnostic value, since it would classify virtually all patients with SLE, SSc, or SS as ANA positive. Conversely, a high positive cutoff at 1:160 serum dilution (high specificity, low sensitivity) would be useful to confirm the presence of disease in only a portion of cases, but would be likely to exclude 95% of normal individuals. CONCLUSION: It is recommended that laboratories performing immunofluorescent ANA tests should report results at both the 1:40 and 1:160 dilutions, and should supply information on the percentage of normal individuals who are positive at these dilutions. A low-titer ANA is not necessarily insignificant and might depend on at least 4 specific factors. ANA assays can be a useful discriminant in recognizing certain disease conditions, but can create misunderstanding when the limitations are not fully appreciated.

In cultures of normal human lymphocytes infected with the human retrovirus HTLV-III/LAV, detectable cytoplasmic virus appears and then disappears in a proportion (1 to 10%) of cells, followed by release of virus detected by particulate reverse transcriptase activity, virus antigen assay, and infectivity titer. Virus infection is associated with loss of detectable T4 antigen on infected cells and, ultimately, complete loss of T4+ cells from the culture. Residual non-T4+ cells are not susceptible to a second infection with HTLV-III/LAV, and in cultures of separated cell populations, substantial virus replication occurred in T4+ T cells and minimally, if at all, in non-T4+ cells. We could not detect a disproportionate loss of cell surface phenotype (other than T4) in comparison of infected and noninfected cultures of lymphocytes or purified T4+ T cells when these cultures were monitored with a panel of monoclonal antibodies that detect the major mononuclear cell types (alpha-T11, alpha-T3, alpha-Mo2, alpha-B1), functional T cell subsets (alpha-T8, alpha-Leu-8, alpha-T17), or activated/proliferating cells (alpha-T10, alpha-Ia, alpha-T9, alpha-4F2, alpha-Tac). HTLV-III/LAV replication was quantitatively greatest in lymphocytes stimulated with phytohemagglutinin (PHA) and cultured in the presence of interleukin 2 (IL 2). Once activated by PHA, virus production in nondividing (irradiated) cells was similar to that in nonirradiated cells, but was substantially reduced if radiation was performed before PHA stimulation. Omission of PHA, IL 2, or both resulted in progressively lower amounts of virus replication. However, virus replication was detected and T4+ T cell depletion occurred in all cultures, regardless of medium supplement or radiation. T4+ T cells absorb infectious virus, and the binding of HTLV-III/LAV to the surface of T4+ T cells, but not to non-T4+ cells, was directly demonstrated. Binding is equivalent in activated and nonactivated cells and at 4 degrees and 37 degrees C. Reciprocal inhibition of binding was observed with alpha-T4a monoclonal antibody and virus. Exposure of cells to alpha-T4a before and during HTLV-III/LAV inoculation inhibited subsequent virus replication. We conclude that T4+ T cells are the major target for HTLV-III/LAV replication, that this tropism is related to expression of the T4 antigen that serves as a binding site for virus, that infection is inexorable in T4+ T cells regardless of subset or activation state, and that the activation/proliferative state of the cells is not a necessary determinant of infectivity, but rather, determines the amount of replication that will ensue.