Human alpha beta and gamma delta T cells from unexposed individuals respond to protein antigens of the yeast form of Paracoccidioides brasiliensis

Unconventional T cells - New players in antifungal immunity

Life-threatening invasive fungal diseases (IFD) are increasing in incidence, especially in immunocompromised patients and successful resolution of IFD requires a variety of different immune cells. With the limited repertoire of available antifungal drugs there is a need for more effective therapeutic strategies. This review interrogates the evidence on the human immune response to the main pathogens driving IFD, with a focus on the role of unconventional lymphocytes e.g. natural killer (NK) cells, gamma/delta (γδ) T cells, mucosal associated invariant T (MAIT) cells, invariant natural killer T (iNKT) cells and innate lymphoid cells (ILC). Recent discoveries and new insights into the roles of these novel lymphocyte groups in antifungal immunity will be discussed, and we will explore how an improved understanding of antifungal action by lymphocytes can inform efforts to improve antifungal treatment options.

Prostate Tumor Microenvironment Alters Immune Cells and Prevents Long-Term Survival in an Orthotopic Mouse Model Following flt3-Ligand/CD40-Ligand Immunotherapy

A novel orthotopic metastatic model of mouse prostate cancer was developed using MHC-negative TRAMP-C1P3 (transgenic adenocarcinoma of mouse prostate) cells derived by serial passage of the parental TRAMP-C1 line in mouse prostate glands. TRAMP-C1P3 cells grew efficiently in mouse prostate glands and reproducibly metastasized to draining lymph nodes. Using this model, we show that Fms-like tyrosine kinase-3 ligand (flt3-L) dramatically inhibited growth of preexisting orthotopic TRAMP-C1P3 tumors and the development of metastatic disease. Mice remained in remission for several months following termination of flt3-L treatment but eventually relapsed and died of progressive disease. flt3-ligand treatment induced a pronounced mixed inflammatory cell infiltrate that consisted of CD8alpha-CD4- dendritic cells (CD11c+), macrophages, granulocytes (Gr-1+) and to a lesser extent T cells (CD4+ and CD8+). Dendritic cells isolated from TRAMP-C1P3 tumors were phenotypically immature (CD11c+ B7.2-I-A-CD40-), and this phenotype was also predominant in peripheral organs of mice treated with flt3-L alone or in combination with the DC maturation factor, CD40-L. Diminished expression of TCR-beta, CD3-epsilon, and CD3-zeta was also observed on intratumoral T cells, although these signaling proteins were reexpressed following in vitro culture with IL-2. The TCR/CD3 complex remained intact on peripheral T cells except in mice treated with flt3-L where CD3-zeta loss was observed. In contrast to alphabeta-T cells, tumor-infiltrating gammadelta-T cells maintained expression of their antigen receptors but not CD3epsilon. Thus, TRAMP-C1P3 tumors quickly establish a microenvironment that profoundly diminishes expression of molecules critical for normal dendritic cell and T cell function, thus limiting the efficacy of flt3-L and CD40-L immunotherapy. Overall, these data suggest that long-term cures of established MHC-negative tumors may not be achieved until therapeutic interventions are engineered to overcome this immunosuppressive microenvironment.

Naive human alpha beta T cells respond to membrane-associated components of malaria-infected erythrocytes by proliferation and production of interferon-gamma

Crude extracts of Plasmodium falciparum schizont-infected erythrocytes (PfSE) induce polyclonal activation of peripheral blood T lymphocytes from naive (malaria unexposed) humans. We demonstrate that the active component of PfSE is membrane bound, soluble in sodium dodecyl sulphate (SDS) and partially heat stable, but distinct from the tumour necrosis factor (TNF)-inducing, exoantigen-like activity of schizont extracts. Malaria pigment induces little or no T-cell activation. The responding cells are predominately CD4+, CD45RO+, T-cell receptor (TCR) alpha beta+. Contrary to previous reports, expansion of the TCR gamma delta+ subset was observed in cells from only one of eight donors. Proliferating cells secrete interferon-gamma (IFN-gamma) and release large amounts of soluble interleukin-2R (sIL-2R) into the culture supernatant but produce no detectable interleukin-4 (IL-4), a phenotype typical of the T-helper (Th)1 subset of CD4+ T cells. We propose that these activated T cells may initiate the inflammatory response to malaria infection in non-immunes and may contribute to the pathology of the disease.

Human gamma/delta T-cell response to Listeria monocytogenes protein components in vitro

Listeria monocytogenes is a facultative intracellular pathogen that replicates inside mononuclear phagocytes and induces specific cellular immunity. Listeriosis encompasses many clinical syndromes and meningitis is the most frequent clinical manifestation. Human alpha/beta and gamma/delta T cells have been shown to respond to L. monocytogenes antigens and to play an important role in resistance against listerial infection. We investigated the nature of listerial ligands and the influence of the major virulence factor, listeriolysin (hly), on the stimulation of human gamma/delta T cells from healthy individuals. We found that a listerial somatic protein ligand, which is sensitive to proteinase treatment, stimulated gamma/delta T cells in vitro; the majority of Listeria-responsive gamma/delta T cells expressed V gamma 9V delta 2 T-cell receptor chains and human leucocyte antigen-DR molecules; gamma/delta T-cell responses to hly+ and hly- Listeria strains were comparable; L. monocytogenes strains of different virulence stimulated gamma/delta T cells equally. Thus, protein components of L. monocytogenes unrelated to virulence activate human gamma/delta T cells in vitro.

Paracoccidioides brasiliensis-stimulated human gamma/delta T cells support antibody production by B cells

Paracoccidioidomycosis patients show hyperactive humoral immune responses. Consequently, we investigated whether cytokines in supernatants from Paracoccidioides brasiliensis-stimulated gamma/delta T cells support B-cell activation. We detected proliferation of B cells and increased immunoglobulin M (IgM) and IgG production. Thus, gamma/delta T cells may participate in polyclonal B-cell activation during paracoccidioidomycosis.