Ligation of the WC1 receptor induces gamma delta T cell growth arrest through fumonisin B1-sensitive increases in cellular ceramide

Molecular Biology of Escherichia Coli Shiga Toxins' Effects on Mammalian Cells

Shiga toxins (Stxs), syn. Vero(cyto)toxins, are potent bacterial exotoxins and the principal virulence factor of enterohemorrhagic Escherichia coli (EHEC), a subset of Shiga toxin-producing E. coli (STEC). EHEC strains, e.g., strains of serovars O157:H7 and O104:H4, may cause individual cases as well as large outbreaks of life-threatening diseases in humans. Stxs primarily exert a ribotoxic activity in the eukaryotic target cells of the mammalian host resulting in rapid protein synthesis inhibition and cell death. Damage of endothelial cells in the kidneys and the central nervous system by Stxs is central in the pathogenesis of hemolytic uremic syndrome (HUS) in humans and edema disease in pigs. Probably even more important, the toxins also are capable of modulating a plethora of essential cellular functions, which eventually disturb intercellular communication. The review aims at providing a comprehensive overview of the current knowledge of the time course and the consecutive steps of Stx/cell interactions at the molecular level. Intervention measures deduced from an in-depth understanding of this molecular interplay may foster our basic understanding of cellular biology and microbial pathogenesis and pave the way to the creation of host-directed active compounds to mitigate the pathological conditions of STEC infections in the mammalian body.

The bovine spleen: interactions among splenic cell populations in the innate immunologic control of hemoparasitic infections

Over the past several years, innate immunity has been recognized as having an important role as a front-line defense mechanism and as an integral part of the adaptive immune response. Innate immunity in cattle exposed to hemoparasites is spleen-dependent and age-related. In this review, we discuss general aspects of innate immunity and the cells involved in this aspect of the response to infection. We also provide examples of specific splenic regulatory and effector mechanisms involved in the response to Babesia bovis, an important tick-borne hemoparasitic disease of cattle. Evidence for the regulatory and effector role of bovine splenic monocytes and DC both in directing a type-1 response through interaction with splenic NK cells and γδT-cells will be presented.

Gamma/Delta T cell mRNA levels decrease at mucosal sites and increase at lymphoid sites following an oral SIV infection of macaques

The oral and esophageal mucosa have been identified as possible sites of HIV/SIV entry following oral infection. Here, gamma/delta (gammadelta) T cells, a multi-functional T cell subset, were assessed at oral/esophageal mucosa and lymphoid sites at the earliest times (1-14 days) post-oral SIV inoculation utilizing quantitative RT-PCR. During these earliest times post-infection, decreased gammadelta TCR mRNA levels were observed at the oral gingiva and esophageal mucosa, while increased levels were observed within regional lymph nodes (cervical and retropharyngeal). Higher lymph node gammadelta TCR levels were associated with increased mRNA expression of the lymphoid homing chemokine/receptor (CCL21/CCR7) pair in these lymph nodes. In contrast to gammadelta TCR levels, CD4 mRNA expression remained relatively stable through 4 days post-infection, and depletion of CD4 T cells was only evident after 7 or 14 days post-infection. The decrease of gammadelta T cell mRNA from mucosal sites and the corresponding increase at lymphoid sites suggest a rapid redistribution of these immune cells at these earliest times post-SIV infection.

Enhanced secretion of interferon-gamma by bovine gammadelta T cells induced by coculture with Mycobacterium bovis-infected dendritic cells: evidence for reciprocal activating signals

Evidence suggests that gammadelta T cells form part of the innate immune response to Mycobacterium bovis infection. Dendritic cells (DCs) are capable of secreting high levels of interleukin-12 (IL-12) following infection with mycobacteria and can induce interferon-gamma (IFN-gamma) secretion by natural killer and gammadelta T cells We investigated the innate interactions occurring between WC1(+)gammadelta T cells and M. bovis-infected DCs. Following coculture with M. bovis-infected DCs, secretion of IFN-gamma and expression of CD25 and major histocompatibility complex class II on WC1(+)gammadelta T cells were significantly enhanced. Reciprocal enhancement of IL-12 secretion by the DCs was also observed and this interaction was found to be contact dependent. We hypothesize that there is an early, transient signal between the WC1(+)gammadelta T cells and the DCs, which promotes the synthesis of biologically active IL-12, and which is dependent upon cell-cell contact. Reciprocal signals including IL-12 are then delivered to WC1(+)gammadelta cells, which leads to the enhanced secretion of IFN-gamma, and the up-regulation of activation markers and antigen presentation molecules by the WC1(+)gammadelta T cells. These interactions are likely to form a critical part of the T helper type 1-conditioning response of DCs to M. bovis.

Bovine WC1(-) gammadeltaT cells incubated with IL-15 express the natural cytotoxicity receptor CD335 (NKp46) and produce IFN-gamma in response to exogenous IL-12 and IL-18

The gammadeltaT cells of ruminants are believed to participate in innate immunity and have been described with regulatory, inflammatory and cytotoxic functions. Here we describe a subset of CD3(+) TcR1(+) WC1(-)gammadeltaT cells expressing CD335 (NKp46), classically associated with CD3(-) natural killer (NK) cells, as a consequence of incubation with IL-15. This population, undetectable at the time of collection, developed after 2 week of IL-15 culture from splenic leukocytes (SPL) reaching greater than 50% of the total gammadeltaT cells. However, they did not grow well from peripheral blood leukocytes (PBL). Splenic gammadeltaT cells positively selected by magnetic separation prior to incubation with IL-15 and analyzed by flow cytometry, consistently yielded CD3(+) cells expressing CD335. These cells arose from the CD335(-)gammadeltaT cell population suggesting that the new population represents up-regulation of CD335 by gammadeltaT cells. CD335 mRNA expression from sorted IL-15-incubated SPL CD335(+)gammadeltaT cells or NK cells exceeded that of CD335(-)gammadeltaT cells. Incubation with IL-12 and IL-18 increased the number of CD335(+)gammadeltaT cells in both the PBL and SPL fractions as compared to controls or IL-12 or IL-18 alone. In addition, CD335(+)gammadeltaT cells demonstrated a robust ability to produce IFN-gamma in response to exogenous IL-12 and IL-18. Taken as a whole, we describe a new phenotypically distinct bovine gammadeltaT cell sub-population capable of participating in type 1 immune responses.

Porcine γδ T cells: Possible roles on the innate and adaptive immune responses following virus infection

gammadelta T cells recognise different types of antigen in alternative ways to alphabeta T cells, and thus appear to play a complementary role in the immune response. However, unlike alphabeta T cells, the role or function of gammadelta T cells is still unclear. As pigs possess a high proportion of circulating gammadelta T cells, they are suitable large animal model to study gammadelta T cell functions. This as yet has not been fully exploited, leaving porcine gammadelta T cell biology and its role in immunity in its infancy. Foot-and-mouth disease (FMD) high potency "emergency" vaccines are able to induce early protection from challenge and it has been suggested that, in part, there is some involvement of innate immune responses. The antigen component of the vaccine is able to stimulate purified naive pig gammadelta T cells and induce the mRNA of various cytokines and chemokines. This observation suggests that gammadelta T cells probably contribute to the early phase of the immune responses to FMD vaccination, and perhaps infection. A subset of these circulating gammadelta T cells display a phenotype similar to professional antigen presenting cells and are able to take up and present soluble antigen to CD4(+) T cells in a direct cell-cell interaction via MHC class II. This direct interaction between gammadelta T cells and CD4(+) T cells is likely to have a significant influence on the out come of the adaptive immune response.

Impact of polyunsaturated fatty acids on cytoskeletal linkage of L-selectin

Polyunsaturated fatty acid [omega-3 polyunsaturated fatty acids (omega-3PUFAs)] incorporation into cell membranes has been shown to have potent anti-inflammatory activity, though the mechanisms involved are only partially characterized. Here, we show that PUFA enrichment of T cell membranes decreased the overall expression of L-selectin as well as a highly conserved epitope on L-selectin that may serve as a marker for optimal protein function. Additionally, PUFA enrichment inhibited L-selectin cytoskeletal association, which is thought to be important for optimal functional activity. In support of this, PUFA enrichment of gammadelta T cell membranes reduced L-selectin-dependent rolling interactions under conditions mimicking physiological flow. Taken together, these data suggest that the anti-inflammatory activity of omega-3 polyunsaturated fatty acids may be due, in part, to a novel effect on L-selectin, namely PUFA reduction or prevention of cytoskeletal association of L-selectin.

Ceramide: does it matter for T cells?

Ceramide and its derivatives have been implicated in cellular activation, differentiation, survival and death. Although the main biological function of ceramide appears to be linked to its potency to induce cell death, its actual relevance as a regulator of cell death has been the subject of controversial discussions. Here, we discuss the significance of ceramide in T-cell biology, with special emphasis on the regulation of T-cell receptor expression, growth arrest, costimulation and death.