Mycobacterium avium complex infection in mice: lack of exacerbation after LP-BM5 murine leukemia virus infection.

The murine leukemia virus LP-BM5 has been used to reproduce the model of murine AIDS in order to evaluate the course of infection with the MO-1 strain of Mycobacterium avium complex (MAC). LP-BM5 was inoculated in C57BL/6 mice by intravenous (i.v.) injection either 8 weeks before an i.v. challenge with 10(3) or 10(6) CFU of MAC (coinfection 1) or 10 days after an i.v. challenge with 10(3) CFU of MAC (coinfection 2). During coinfection 2 experiments, the phenotypic alterations in blood lymphocyte subsets were analyzed. During coinfection 1, LP-BM5 infection tended to decrease the mycobacterial growth, with the difference reaching statistical significance for the lower inoculum (10(3) CFU of MAC) (P<0.001). During coinfection 2, LP-BM5 did not exacerbate MAC infection except in the spleen, at day 90 after LP-BM5 challenge (P<0.001). LP-BM5 infection and the LP-BM5-MAC coinfection increased the numbers of activated CD4+ lymphocytes (CD4+ Ly6AE+) (P<0.001), activated CD8+ lymphocytes (CD8+ Ly6AE+) (P<0.001), and activated B lymphocytes (Ly5+ Ly6AE+) (P<0.001). This activation of T lymphocytes could explain the lack of exacerbation of MAC infection and even the trend to a lower level of MAC infection. Thus, this model of retroviral infection of mice does not seem to be a reliable model of immunodepression for the study of MAC infection and its treatments.

Correlation of CD8 lymphocyte activation with cellular viremia and plasma HIV RNA levels in asymptomatic patients infected by human immunodeficiency virus type 1.

The relationship between CD8 lymphocyte phenotypic alterations and virological parameters was studied in 47 asymptomatic subjects with human immunodeficiency virus type 1 (HIV-1) infection and CD4 T cell counts above 400/microliters. CD8 subsets were examined by means of three-color flow cytometry, using an extensive panel of monoclonal antibody combinations. Virological parameters were measured by both end-point dilution culture of peripheral blood mononuclear cells (PBMCs) and plasma and branched-DNA (bDNA) signal amplification of plasma HIV RNA. Whereas HIV-infected patients had a near-normal CD4 cell count (mean, 782 cells/microliter), several subsets of activated CD8 cells were markedly expanded relative to values in 23 HIV-seronegative controls. The PBMC cultures were positive in 38 cases and plasma HIV RNA was detected in 31. The percentage of CD4 cells correlated negatively with both cellular viremia and plasma HIV RNA levels. Conversely, a positive correlation was observed between viral load and the percentage of CD8 cells. Among CD8 lymphocytes, the CD38+CD8 and HLA-DR+CD8 subsets correlated best with viral load. Three-color analysis showed that the subpopulations involved in this relationship were CD38+HLA-DR+, CD38+CD28-, HLA-DR+CD28+, HLA-DR+CD57-, CD38+CD57-, CD38+CD45RO+, and HLA-DR+CD45RO+. Our data provide the first evidence that viral load correlates with subsets of activated CD8 lymphocytes in asymptomatic HIV-infected subjects who have near-normal numbers of CD4 lymphocytes.

Interactions between murine AIDS (MAIDS) and toxoplasmosis in co-infected mice.

We coinfected C57B1/6 mice with LP-BM5 murine leukaemia viruses, responsible for murine AIDS (MAIDS), and an avirulent strain of Toxoplasma gondii. Virus-infected mice were infected perorally on day 30 with 10 cysts of T. gondii, and T. gondii-infected mice were challenged with LP-BM5 on day 20, 30 or 60 after parasite inoculation. Uninfected and singly infected mice were used as controls. The kinetics of parasite burden in blood, lungs and brain, together with blood lymphocyte subsets, and spleen and lymph node weights, were serially determined in each group of mice. The kinetics of parasite counts in mice infected by LP-BM5 then by T. gondii were similar to those in mice infected by T. gondii only, except for lung counts, which reached higher values than in animals infected with T. gondii alone, then fell and re-increased until the end of the experiment. The only significant change in parasite burdens when mice were first infected by T. gondii and then by LP-BM5, compared with T. gondii controls, was an increase in lung counts in mice challenged with LP-BM5 20 days after T. gondii inoculation. Whatever the schedule of co-infection, the kinetics of lymphocyte subsets in co-infected mice differed from those in T. gondii- or LP-BM5-infected mice; in dually infected mice CD4+ and CD8+ cell counts were intermediate between values in mice singly infected by the parasite or the virus. Enlargement of spleen and lymph nodes, which is a major criterion of MAIDS progression, was significantly less marked in co-infected mice than in mice infected with LP-BM5 alone. These data point to cross-regulation of T. gondii and LP-BM5 infections, which results in increased susceptibility to T. gondii, and may alter the progression of MAIDS.

Toxoplasma gondii: kinetics of lymphocyte subsets in blood and spleen of perorally infected mice.

The blood and spleen lymphocyte subsets and parasite burdens in blood, lungs, and brain were determined serially in C57B1/6 mice infected with an avirulent strain of Toxoplasma gondii. Five mice were sacrificed at various time points after infection; Thy1-2+, Ly5+, CD4+, CD8+, and Ly6c+ lymphocyte subsets and macrophages were determined in blood and spleen by cytofluorometry and parasite burdens were quantified in blood, lungs, and brain by means of a tissue culture method. In infected mice, a large increase in the percentage of CD8+ lymphocytes in blood was observed from Day 14, peaking at Day 21; the percentage of CD4+ lymphocytes was not significantly modified compared with uninfected controls. Analysis of Ly6 antigen expression on T lymphocytes showed that CD8+Ly6c+ cells were largely predominant at the different stages of infection. Similar results were obtained for spleen cells. The marked increase in CD8+Ly6c+ cells in the early phase of infection was associated with the clearance of parasites from the lungs. Furthermore, the proportion of CD8+Ly-6c+ remained high until Day 162, when the infection was at the chronic stage. These results suggest that CD8+Ly6c+ lymphocytes may be involved in the control of toxoplasmosis in the acute phase and in the containment of the infection in the chronic stage.

Prognostic value of phenotypic alterations in blood lymphocyte subsets in a murine retrovirus-induced immunodeficiency syndrome (MAIDS).

Mice infected with the Duplan strain of murine leukaemia virus (Dup MuLV), a retrovirus, develop a syndrome sharing several features with AIDS, including lymphadenopathy and profound immunodeficiency. We measured the changes in peripheral blood lymphocyte populations and evaluated their predictive value for the outcome of disease in C57Bl/6 mice. Animals were inoculated with Dup MuLV (SC1/Dup MuLV confluent fibroblast supernatant or spleen extract from an infected mouse). Peripheral blood lymphocyte subsets were sequentially monitored for 73 days using flow cytometric analysis and MoAbs directly conjugated to fluorochromes. A striking fall in the Thy1.2+ cell count occurred in diseased animals, mostly affecting the CD8+ cell compartment. At the same time, the percentage of Ly5+ cells was increased. Mice were killed at day 73 and spleen and lymph node lymphocytes were analysed. Phenotypic lymphocyte modifications in peripheral blood were closely related to those in the spleen or lymph nodes. Analysis of Ly6c antigen expression on CD4+ and CD8+ cells showed a selective expansion of the CD8+Ly6c+ subset, which may reflect a state of immune activation. Our results suggest that phenotypic alterations of peripheral blood lymphocytes are a good marker of disease progression in this model and could be a useful criterion to evaluate antiretroviral therapy.