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T cells use the endocytic pathway for key cell biological functions, including receptor turnover and maintenance of the immunological synapse. Some of the established players include the Rab GTPases, the SNARE complex proteins, and others, which function together with EPS-15 homology domain-containing (EHD) proteins in non-T cell systems. To date, the role of the EHD protein family in T cell function remains unexplored. We generated conditional EHD1/3/4 knockout mice using CD4-Cre and crossed these with mice bearing a myelin oligodendrocyte glycoprotein-specific TCR transgene. We found that CD4 + T cells from these mice exhibited reduced Ag-driven proliferation and IL-2 secretion in vitro. In vivo, these mice exhibited reduced severity of experimental autoimmune encephalomyelitis. Further analyses showed that recycling of the TCR-CD3 complex was impaired, leading to increased lysosomal targeting and reduced surface levels on CD4 + T cells of EHD1/3/4 knockout mice. Our studies reveal a novel role of the EHD family of endocytic recycling regulatory proteins in TCR-mediated T cell functions., (Copyright © 2018 by The American Association of Immunologists, Inc.)

Nitrated alpha-synuclein (N-alpha-syn) immunization elicits adaptive immune responses to novel antigenic epitopes that exacerbate neuroinflammation and nigrostriatal degeneration in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of Parkinson's disease. We show that such neuroimmune degenerative activities, in significant measure, are Th17 cell-mediated, with CD4(+)CD25(+) regulatory T cell (Treg) dysfunction seen among populations of N-alpha-syn-induced T cells. In contrast, purified vasoactive intestinal peptide induced and natural Tregs reversed N-alpha-syn T cell nigrostriatal degeneration. Combinations of adoptively transferred N-alpha-syn and vasoactive intestinal peptide immunocytes or natural Tregs administered to MPTP mice attenuated microglial inflammatory responses and led to robust nigrostriatal protection. Taken together, these results demonstrate Treg control of N-alpha-syn-induced neurodestructive immunity and, as such, provide a sound rationale for future Parkinson's disease immunization strategies.

Microglial inflammatory neuroregulatory activities affect the tempo of nigrostriatal degeneration during Parkinson's disease (PD). Such activities are induced, in part, by misfolded, nitrated alpha-synuclein (N-alpha-syn) within Lewy bodies released from dying or dead dopaminergic neurons. Such pathobiological events initiate innate and adaptive immune responses affecting neurodegeneration. We posit that the neurobiological activities of activated microglia are affected by cell-protein and cell-cell contacts, in that microglial interactions with N-alpha-syn and CD4(+) T cells substantively alter the microglial proteome. This leads to alterations in cell homeostatic functions and disease. CD4(+)CD25(+) regulatory T cells suppress N-alpha-syn microglial-induced reactive oxygen species and NF-kappaB activation by modulating redox-active enzymes, cell migration, phagocytosis, and bioenergetic protein expression and cell function. In contrast, CD4(+)CD25(-) effector T cells exacerbate microglial inflammation and induce putative neurotoxic responses. These data support the importance of adaptive immunity in the regulation of Parkinson's disease-associated microglial inflammation.

HIV-1-associated neurocognitive impairments are intrinsically linked to microglial immune activation, persistent viral infection, and inflammation. In the era of antiretroviral therapy, more subtle cognitive impairments occur without adaptive immune compromise. We posit that adaptive immunity is neuroprotective, serving in both the elimination of infected cells through CD8(+) cytotoxic T cell activities and the regulation of neuroinflammatory responses of activated microglia. For the latter, little is known. Thus, we studied the neuromodulatory effects of CD4(+) regulatory T cells (Treg; CD4(+)CD25(+)) or effector T cells in HIV-1-associated neurodegeneration. A newly developed HIV-1 encephalitis mouse model was used wherein murine bone marrow-derived macrophages are infected with a full-length HIV-1(YU2)/vesicular stomatitis viral pseudotype and injected into basal ganglia of syngeneic immunocompetent mice. Adoptive transfer of CD3-activated Treg attenuated astrogliosis and microglia inflammation with concomitant neuroprotection. Moreover, Treg-mediated anti-inflammatory activities and neuroprotection were associated with up-regulation of brain-derived neurotrophic factor and glial cell-derived neurotrophic factor expression and down-regulation of proinflammatory cytokines, oxidative stress, and viral replication. Effector T cells showed contrary effects. These results, taken together, demonstrate the importance of Treg in disease control and raise the possibility of their utility for therapeutic strategies.

The thymus dependency of murine intestinal intraepithelial lymphocytes (IEL) was studied in an athymic F1----parent radiation chimera model. IEL, although not splenic or lymph node lymphocytes, from athymic chimeras displayed normal levels of cells bearing the class-specific T cell Ag, CD4 and CD8; the TCR-associated molecule, CD3; and the Thy-1 Ag. Moreover, two-color flow cytometric analyses of IEL from athymic mice demonstrated regulated expression of T cell Ag characteristic of IEL subset populations from thymus-bearing mice. In immunoprecipitation experiments, surface TCR-alpha beta or TCR-gamma delta were expressed on IEL, although not on splenic lymphocytes, from athymic chimeras. That IEL from athymic chimeras constituted a population of functionally mature effector cells activated in situ, similar to IEL from thymus-bearing mice, was demonstrated by the presence of CD3-mediated lytic activity of athymic lethally irradiated bone marrow reconstituted IEL. These data provide compelling evidence that intestinal T cells do not require thymic influence for maturation and development, and demonstrate that the microenvironment of the intestinal epithelium is uniquely adapted to regulate IEL differentiation.

Frequently, patients with systemic cryptococcosis have depressed or absent in vivo or in vitro cell-mediated immune responses to cryptococcal antigen. In addition, these patients have relatively high levels of circulating cryptococcal antigen, which is generally considered indicative of a poor prognosis. Because acquired cell-mediated immunity is an important host defense mechanism in cryptococcosis, we have been studying the effects of cryptococcal antigen on such responses. Using a murine model, we have demonstrated that cryptococcal antigen given i.v. to CBA/J mice, to simulate antigen levels found in patients, can trigger the production of a series of suppressor cells that specifically inhibit anticryptococcal cell-mediated immune responses. Briefly, cryptococcal antigen induces afferent suppressor and/or suppressor inducer (Ts1) cells in the lymph nodes of mice, and the Ts1 cells, or a soluble factor derived therefrom (TsF1), stimulate the production of second-order or efferent suppressor (Ts2) cells. This report provides data that demonstrate that the Ts2 cells were induced in spleens from cyclophosphamide (Cy)-resistant precursors in response to cryptococcal Ts1 cells or TsF1 and that a proliferative process sensitive to Cy was not required for Ts2 induction. The Ts2 cells were detectable 6 days after Ts1 injection, were specific in suppressing the cryptococcal delayed-type hypersensitivity (DTH) response, were T cells with an Lyt-1-,2+,Ia+ (I-J+) phenotype, were effective only on the efferent limb of the cryptococcal DTH response, and mediated their activity via a soluble factor (TsF2). Thus far, the suppressive pathway induced by cryptococcal antigen has characteristics more like those of the suppressor circuits described for the DTH responses to the haptens azobenzenearsonate and 4-hydroxy-3-nitrophenyl acetyl than those of the modulating circuits induced by other antigens. We postulate that a suppressive circuit similar to the one we have defined in the mouse model is operating to suppress the in vivo and in vitro cell-mediated immune responses in cryptococcosis patients who have significant amounts of circulating cryptococcal antigen.

Cryptococcosis patients frequently have high levels of cryptococcal antigen in their body fluids, and the levels of circulating antigen can generally be used to predict the patient's recovery, with high or rising antigen titers indicating a poor prognosis and low or decreasing levels a good prognosis. In a previous study, we reported on a murine model for studying the effects of cryptococcal antigen on host defense mechanisms. In that work, we demonstrated that an i.v. injection of cryptococcal antigen (CneF) into CBA/J mice, to simulate the antigenemia known to occur in human cryptococcosis, induced a population of T suppressor cells (Ts1) in the lymph nodes (LN). Upon adoptive transfer, the Ts1 cells specifically suppressed the afferent limb of the delayed-type hypersensitivity (DTH) response to cryptococcal antigen. In the present study, we show that the precursors of the Ts1 cells are sensitive to low-dose cyclophosphamide treatment and that the phenotype of the Ts1 cells is Lyt-1+, Ia+ (I-J+). LN cells from CneF-injected mice or a soluble factor derived therefrom can induce in the spleens of recipient mice a second-order suppressor cell population that suppresses the efferent limb of the DTH response. The cells that induce the second-order or efferent suppressor cells have the same phenotype as the cells that appear to suppress the afferent limb of the DTH response. The findings in this study indicate that a complex regulatory mechanism is responsible for the observed suppression of the DTH response in this infectious disease model. Furthermore, the suppressive circuit thus far defined for cryptococcal antigen is similar to the antigen-specific suppressor cell pathway outlined for certain chemically defined haptenic systems.