Increased level of activated gamma delta lymphocytes correlates with disease severity in HIV infection

Increased frequency of systemic pro-inflammatory Vδ1+ γδ T cells in HIV elite controllers correlates with gut viral load

γδ T cells predominate in the intestinal mucosa and help maintain gut homeostasis and mucosal immunity. Although HIV infection significantly alters these cells, what drives these perturbations is unclear. Growing evidence suggests that impaired intestinal immune function in HIV leads to chronic immune activation and disease progression. This occurs even in HIV controllers - individuals with undetectable HIV viremia without antiretroviral therapy (ART). We show that Vδ1⁺ cells, a subset of γδ T cells described as being important in intestinal barrier function, increase in frequency in HIV-infected individuals, including HIV controllers. These cells resemble terminally differentiated effector memory cells, producing the pro-inflammatory cytokines IFNγ, TNFα, and MIP-1β upon stimulation. Importantly, pro-inflammatory Vδ1⁺ cell frequency correlates with levels of HIV RNA in intestinal tissue but not in plasma. This study supports a model in which local viral replication in the gut in HIV controllers disrupts the phenotype and function of Vδ1⁺ cells, a cell type involved in the maintenance of epithelial barrier integrity, and may thereby contribute to systemic immune activation and HIV disease progression.

HIV infection deregulates innate immunity to malaria despite combination antiretroviral therapy

OBJECTIVE

Malaria and HIV-1 adversely interact, with HIV-positive individuals suffering higher parasite burdens and worse clinical outcomes. However, the mechanisms underlying these disease interactions are unclear. We hypothesized that HIV coinfection impairs the innate immune response to malaria, and that combination antiretroviral therapy (cART) may restore this response. Our aim was to examine the innate inflammatory response of natural killer (NK), natural killer T (NKT), and γδ T-cells isolated from the peripheral blood of HIV-infected therapy-naive donors to malaria parasites, and determine the effect of cART on these responses.

METHODS

Freshly isolated peripheral blood mononuclear cells from 25 HIV-infected individuals pre-cART (month 0) and post-cART (months 3 and 6), and HIV-negative individuals at matched time-points, were cultured in the presence of Plasmodium falciparum parasitized erythrocytes. Supernatants and cells were collected to assess cytokine production and phenotypic changes.

RESULTS

Compared to HIV-negative participants, NKT, NK, and γδ T-cell subsets from participants with chronic HIV infection showed marked differences, including decreased production of interferon γ (IFNγ) and tumor necrosis factor (TNF) in response to malaria parasites. IFNγ production was linked to interleukin-18 receptor (IL-18R) expression in all three cell types studied. Six months of cART provided partial cellular reconstitution but had no effect on IL-18R expression, or IFNγ and TNF production.

CONCLUSION

These data suggest that HIV infection impairs the inflammatory response of innate effector cells to malaria, and that the response is not fully restored within 6 months of cART. This may contribute to higher parasite burdens and ineffective immune responses, and have implications for vaccination initiatives in coinfected individuals.

Phenotypic analysis of peripheral blood gammadelta T lymphocytes and their targeting by human immunodeficiency virus type 1 in vivo

There is increasing evidence that a wider range of lymphoid cell types other than CD4(+) T helper lymphocytes are infected with HIV-1 in vivo, including CD8 lymphocytes, natural killer cells, and reticulodendritic cells. Each potentially contributes to the reservoir of infected cells that resist antiviral treatment and to the impairment of immune responses in AIDS. By quantitative PCR for HIV proviral sequences we have now obtained evidence for substantial infection of gammadelta lymphocytes, contributing 3-45% of the proviral load in peripheral blood. A large proportion of gammadelta lymphocytes constitutively expressed the chemokine receptors CCR5 and CXCR4, with evidence for marked up-regulation of CD8 in samples from HIV-infected individuals, corresponding to an activated phenotype. That gammadelta lymphocytes might be susceptible to HIV infection was investigated using in vitro infectivity assays of recombinant HIV-expressing green fluorescent protein, followed by flow cytometry. gammadelta, CD4, and CD8 lymphocytes were each productively infected, with gammadelta lymphocytes showing the greatest susceptibility. For each cell type, blocking assays with an anti-CD4 monoclonal antibody indicated that entry was CD4-dependent.

T cell receptor usage in patients with non-progressing HIV infection

It is still unclear why some patients with HIV progress more slowly than others to developing full blown AIDS. In this study using flow cytometry we have investigated the TCRBV repertoire of peripheral blood T lymphocytes in 17 long-term non-progressing HIV patients (LTNP) to determine if there is a biased usage of T cell receptor V gene products. Patients were identified from hospital records and entered into the study. Three colour flow cytometry was used to determine the expression of the TCRBV3S5, BV5S1, BV5S2, BV5S3, BV6S1, BV7S1, BV9, BV11, BV12, BV13, BV14, BV16, BV17, BV18, BV20, BV21S3, BV22, and BV23 by CD8 and CD4 positive cells isolated from the peripheral blood of patients and controls. Increases in the absolute numbers of CD8+ T cells expressing TCRBV2 and 8 were observed in the HIV-LTNP population (P < 0.05 in both cases). No differences were seen in numbers of CD8+ T cells expressing other TCRBV or in any TCRBV within the CD4+ T cell popu-lation. At follow up (1-2 years later), those patients in which CD4 levels were below 500 x 106/l were those initially found to have lower levels of TCRBV8 +ve CD8 cells. A significant increase in the absolute numbers of T cells coexpressing the gamma delta (gammadelta) T cell receptor and CD8 were also seen in the HIV-LTNP patients compared with controls (P = 0.002). The increase in CD8+ T cells in the HIV-LTNP patients may be interpreted as either an antigen specific, or group of antigen specific responses to viral antigen, or less likely a viral superantigen. A low level of TCRBV8, CD8+ T cells might be predictive of a more rapid disease progression and might indicate a protective role for this population in HIV infected patients. The increase in gammadeltaT cells bearing the CD8 coreceptor suggests a role for this cell type in the response to HIV infection.

The dominant source of CD4+ and CD8+ T-cell activation in HIV infection is antigenic stimulation

To distinguish between antigenic stimulation and CD4+ T-cell homeostasis as the cause of T-cell hyperactivation in HIV infection, we studied T-cell activation in 47 patients before and during highly active antiretroviral therapy (HAART). We show that expression of human leukocyte antigen (HLA)-DR, CD38, and Ki67 on T cells decreased during HAART but remained elevated over normal values until week 48 of therapy. We confirm previous reports that T-cell activation correlates positively with plasma HIV RNA levels (suggesting antigenic stimulation), and negatively with CD4 count (suggesting CD4+ T-cell homeostasis). However, these correlations may be spurious, because misleading, due to the well-established negative correlation between CD4 count and plasma HIV RNA levels. To resolve this conflict, we computed partial correlation coefficients. Correcting for CD4 counts, we show that plasma HIV RNA levels contributed to T-cell hyperactivation. Correcting for plasma HIV RNA levels, we show that CD4+ T-cell depletion contributed to T-cell activation. Correcting for both, activation of CD4+ and CD8+ T cells remained positively correlated. Because this suggests that CD4+ and CD8+ T-cell activation is caused by a common additional factor, we conclude that antigenic stimulation by HIV or other (opportunistic) infections is the most parsimonious explanation for T-cell activation in HIV infection. Persistence of HIV antigens may explain why T-cell activation fails to revert to levels found in healthy individuals after 48 weeks of therapy.

Topical and systemic therapy for recurrent aphthous stomatitis

The cause of recurrent aphthous ulcers (RAU), the lesions of recurrent aphthous stomatitis, is incompletely understood but appears to involve immune system dysfunction. Treatment options include no treatment, treatment of associated systemic diseases or conditions (eg, celiac sprue, vitamin deficiencies), systemic medications, topical medications, conversion of the aphthous ulcer to a wound, and palliative treatments. The most effective treatments (systemic or topical corticosteroids, thalidomide) involve agents that suppress or modulate immune system function. In general, topical agents are preferred because they have fewer associated side effects; however, inability to obtain adequate contact time may limit their effectiveness. Adjunct pain control is sometimes necessary, either with pain medications or with adherent agents that coat the ulcers.

Oral ulceration in HIV infection: investigation and pathogenesis

Oral ulcerations associated with HIV infection include recurrent aphthous ulcers (RAU). Whereas RAU prevalence is not increased, lesion severity is: among a group of HIV+ patients, 66% had the more severe herpetiform or major RAU. This increased severity suggests that HIV disease-related changes in the immune system may exacerbate RAU. In the peripheral blood of healthy subjects with RAU, CD4:CD8 cell ratios may be reversed and the proportion of T cell receptor-gamma delta + cells increased. HIV disease-related immune system changes are characterized by reversed CD4:CD8, lowered CD4 cell counts and an inverse correlation between CD4 cell counts and per cent activated gamma delta lymphocytes. Adhesion molecules and cytokines involved in lymphocyte homing may be important in RAU pathogenesis: ICAM-I and ELAM are strongly expressed, and TNF alpha production is increased in peripheral blood lymphocytes of healthy patients with RAU. In patients with active HIV disease/AIDS, serum TNF alpha levels are increased. Thalidomide, which inhibits TNF alpha production, is effective treatment for RAU. Some RAU patients have vitamin B12 or folate deficiencies, levels of which are commonly low in HIV+/AIDS patients. However, in a case control study of HIV+ patients, vitamin B12- or folate-deficiencies were not found to be significant risk factors for RAU.

Gamma delta T-cell help in responses to pathogens and in the development of systemic autoimmunity

Mice rendered deficient in alpha beta T-cells by single-gene knockout mutation show enhanced levels of autoantibody formation and even some symptoms of autoimmune disease. This is remarkable given that most experimental studies heretofore have indicated that the development of autoimmune disease is highly multigenic, requiring the complementary actions of multiple loci. The basis of the phenomenon in alpha beta T-cell-deficient mice appears to be the provision of help to B-cells by other cells, including gamma delta T-cells. Perhaps surprisingly, gamma delta T-cell help seems quite efficacious, particularly after infection, when it can culminate in the formation of germinal centers. Furthermore, two independent sets of studies reviewed here indicate that significant levels of self-reactive IgG can also be provoked by gamma delta T-cells independent of germinal center formation. The task ahead is to integrate this pathway into the physiologic immune responses to healthy individuals, immunocompromised individuals, and newborns.