The role of WC1(+) gamma delta T-cells in the delayed-type hypersensitivity (DTH) skin-test reaction of Mycobacterium bovis-infected cattle

Identifying Bacterial and Host Factors Involved in the Interaction of Mycobacterium bovis with the Bovine Innate Immune Cells

Bovine tuberculosis is an important animal and zoonotic disease caused by Mycobacterium bovis. The innate immune response is the first line of defense against pathogens and is also crucial for the development of an efficient adaptive immune response. In this study we used an in vitro co-culture model of antigen presenting cells (APC) and autologous lymphocytes derived from peripheral blood mononuclear cells to identify the cell populations and immune mediators that participate in the development of an efficient innate response capable of controlling the intracellular replication of M. bovis. After M. bovis infection, bovine immune cell cultures displayed upregulated levels of iNOS, IL-22 and IFN-γ and the induction of the innate immune response was dependent on the presence of differentiated APC. Among the analyzed M. bovis isolates, only a live virulent M. bovis isolate induced an efficient innate immune response, which was increased upon stimulation of cell co-cultures with the M. bovis culture supernatant. Moreover, we demonstrated that an allelic variation of the early secreted protein ESAT-6 (ESAT6 T63A) expressed in the virulent strain is involved in this increased innate immune response. These results highlight the relevance of the compounds secreted by live M. bovis as well as the variability among the assessed M. bovis strains to induce an efficient innate immune response.

Molecular findings and approaches spotlighting Mycobacterium bovis persistence in cattle

Mycobacterium tuberculosis (Mtb) and Mycobacterium bovis (M. bovis) are the etiological agents of human and bovine tuberculosis (TB, bTB) respectively, and share genetic identity over 99% at the whole genome level. Progress has been made towards explaining how mycobacteria and their infected hosts remain in balance without producing clinical symptoms of disease, a phenomenon referred to as latency or persistence, which can be mimicked by certain in vitro conditions. Latency/persistence has mainly been studied using Mtb, where the two-component signalling system, dosRS, has been assigned an instrumental role, and even constitutes the current basis for development of new diagnostic methods and treatment addressing this particular stage of TB. M. bovis conserves homolog genes that in Mtb play a role in human latent TB infection and that, by analogy, would allow it to enter a persistent state in infected cattle; nevertheless, little attention has been paid to this stage in bovine hosts. We suggest that many of the advances acquired through the study of Mtb can and should be taken into consideration by research groups and veterinary professionals dealing with bTB. The study of the infection in bovines, paying particular attention to defining the molecular and cellular markers of a M. bovis persistent infection in cattle, presents great opportunities for the development and trial of new diagnostic tests and vaccines, tools that will surely help in promoting eradication of bTB in high-burden settings.

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.

Lymphocyte subset distribution in apparently normal and single intradermal test-positive water buffaloes analyzed by flow cytometry

Monoclonal antibodies (mAbs) against bovine lymphocyte cell surface antigens namely, MHC Class I, MHC class II (DP, DQ and DR), CD3, CD4, CD8, gamma delta TCR, WC1N1 and WC1N2, were tested for their reactivity on apparently normal buffalo mononuclear cells prepared from spleen, lymph nodes and peripheral blood. All the mAbs cross-reacted with the buffalo mononuclear cells. The mean (+/-SD) CD4:CD8 cell ratio in the peripheral blood of apparently normal buffaloes was 1.08+/-0.049 while in the spleen and lymph nodes it was 0.90+/-0.080 and 1.81+/-0.430, respectively. The lymphocyte subsets in the buffaloes positive for tuberculosis by the single intra dermal (SID) test was found to be altered; the CD4 cells were reduced while the CD8 and gamma delta cells were increased. The mean CD4:CD8 ratio in the SID positive buffaloes was 0.36+/-0.010.

Vaccination of cattle with a CpG oligodeoxynucleotide-formulated mycobacterial protein vaccine and Mycobacterium bovis BCG induces levels of protection against bovine tuberculosis superior to those induced by vaccination with BCG alone

The development of a subunit protein vaccine for bovine tuberculosis which could be used either in combination with Mycobacterium bovis BCG (to improve the efficacy of that vaccine) or alone would offer significant advantages over currently available strategies. A study was conducted with cattle to determine the protective efficacy of a strategy based on concurrent immunization with an M. bovis culture filtrate (CFP) vaccine and BCG compared to vaccination with either vaccine alone. One group of calves (10 animals per group) was vaccinated subcutaneously with CFP formulated with Emulsigen and combined with a CpG oligodeoxynucleotide (ODN). A second group was vaccinated with both the CFP vaccine and BCG injected at adjacent sites (CFP-BCG). One further group was vaccinated subcutaneously with BCG, while another group served as nonvaccinated control animals. Vaccination with CFP-BCG induced levels of antigen-specific gamma interferon (IFN-gamma) and interleukin-2 (IL-2) in whole-blood cultures that were higher than those induced by vaccination with BCG alone. The combination of CFP and BCG did not enhance the production of antibodies to M. bovis CFP compared to vaccination with CFP alone. Vaccination with CFP alone led to delayed antigen-specific IFN-gamma and IL-2 responses. Vaccination with CFP-BCG induced a high level of protection against an intratracheal challenge with virulent M. bovis, based on a significant enhancement of six pathological and microbiological parameters of protection compared with the nonvaccinated group. In contrast, vaccination with BCG alone induced a significant enhancement of protection in only one parameter, while CFP alone induced no protection. These results suggest that a combination of a CpG ODN-formulated protein vaccine and BCG offers better protection against bovine tuberculosis than does BCG alone.

Ability of T cell subsets and their soluble mediators to modulate the replication of Mycobacterium bovis in bovine macrophages

Peripheral blood mononuclear cells (PBMCs) from cattle vaccinated with Bacillus Calmette-Guerin (BCG) were obtained and expanded in vitro by incubation with purified protein derivative. The ability of these cells to modulate the replication of virulent Mycobacterium bovis in autologous-infected macrophages was compared to cells from non-vaccinated controls. Cells from non-vaccinated animals were shown to confer a significant degree of mycobacteriostatic activity to autologous-infected macrophages. This activity was not inhibited by including a neutralizing antibody versus interferon-gamma (IFN-gamma), and was dependent on direct contact between PBMCs and infected macrophages. Addition of autologous PBMCs from BCG-vaccinated cattle was shown to significantly enhance macrophage resistance to M. bovis, and this increased macrophage resistance was partly abrogated by including a neutralizing antibody to IFN-gamma. Addition of T cells from non-vaccinated animals to infected macrophages was associated with a modest increase in macrophage release of TNF-alpha and nitric oxide, whereas PBMCs from vaccinated animals increased very significantly the release of these factors. Neutralization of nitric oxide (NO), by inclusion of monomethyl-L-arginine, significantly diminished the ability of PBMCs from vaccinated animals to enhance macrophage resistance to M. bovis, but had no impact on the ability of T cells from naive animals to modulate macrophage function. The ability of naive cells to increase macrophage anti-M. bovis activity was largely mediated by CD4+ T cells, whereas both CD4+ T cells and CD8+ T cells conferred macrophage resistance to M. bovis in vaccinated animals. These data highlight the role of IFN-gamma and NO in the immune resistance of cattle to M. bovis.