Cellular mechanisms of anti-mycobacterial immunity

Cytokine and Chemokine Concentrations as Biomarkers of Feline Mycobacteriosis

Mycobacteriosis is an emerging zoonotic disease of domestic cats and timely, accurate diagnosis is currently challenging. To identify differential cytokine/chemokine concentrations in serum/plasma of cats, which could be diagnostic biomarkers of infection we analysed plasma/serum from 116 mycobacteria-infected cats, 16 healthy controls and six cats hospitalised for unrelated reasons was analysed using the Milliplex MAP Feline Cytokine Magnetic Bead multiplex assay. Three cytokines; sFAS, IL-13 and IL-4 were reduced while seven; GM-CSF, IL-2, PDGF-BB, IL-8, KC, RANTES and TNF-α were elevated in mycobacteria-infected cats compared to healthy controls. However, IL-8 and KC concentrations were not significantly different from cats hospitalised for other reasons. Elevations in TNF-α and PDGF-BB may have potential to identify M. bovis and M. microti infected cats specifically while GM-CSF, IL-2 and FLT3L were increased in MTBC infected cats. This study demonstrates potential use of feline tuberculosis as a spontaneously occurring model of this significant human disease. Cytokine profiling has clear diagnostic potential for mycobacteriosis of cats and could be used discriminate tuberculous from non-tuberculous disease to rapidly inform on zoonotic risk. Future work should focus on the in-field utility of these findings to establish diagnostic sensitivity and specificity of these markers.

BCG-induced protection in guinea pigs vaccinated and challenged via the respiratory route

Since studies on cellular immune responses have demonstrated the role of the mucosal lymphoid system of the respiratory tract, we have studied responses obtained from the local respiratory route, compared to the systemic intradermal route, of BCG immunization. Guinea pigs vaccinated with different doses of BCG via both routes served to follow lymphoid cell proliferation, hilar lymph node and lung BCG clearance, lung granuloma formation and protection induced after virulent challenge. Results demonstrate that the aerogenic route of vaccination with BCG has no harmful side-effects for the host. In comparison with the intradermal route of vaccination, aerogenic vaccination with 10(5) BCG cfu induced higher local cellular immune responses and a substantially improved protective effect.

Delayed-type hypersensitivity and immunity to Salmonella typhimurium

Studies were carried out to correlate immunity and expression of delayed-type hypersensitivity (DTH) in mice of the C3H lineage immunized with an avirulent strain of Salmonella typhimurium (strain SL3235). This strain belongs to a class of aroA- organisms which are being considered as vaccine strains for humans and veterinary use. In a systematic study, the relationship between the mouse strain and the immunizing dose of strain SL3235 on the development of protective immunity and DTH was examined. It was found that in hypersusceptible C3H/HeJ and C3HeB/FeJ mice, several doses of strain SL3235 afforded protection against intravenous challenge doses as high as 1,300 50% lethal doses. Despite these significant levels of immunity to challenge, mice of these two strains never mounted significant DTH responses following immunization with the doses of strain SL3235 tested, which spanned 3 orders of magnitude. Nonresponsiveness was not due to antigen overload, as all of the mouse strains were comparably colonized with strain SL3235 at the time of DTH elicitation. Further, it was found that the ability of responsive C3H/HeNCrlBR mice to display DTH was dependent on the immunizing dose of strain SL3235 and that a dosage could be found that resulted in increased resistance to challenge in these mice without a concomitant display of DTH. Thus, while both induction of protective immunity and DTH were vaccine dosage dependent in the responsive mouse strain (C3H/HeNCrlBR), DTH was a less sensitive measure of protective immunity than survival. Vaccine dosages ranging over three orders of magnitude failed to yield positive footpads to the Salmonella elicitin in the nonresponsive mice. The data suggest that caution should be observed in interpreting Salmonella DTH tests that are used as screens of immune status to typhoid fever in humans, as the extent of discordance between immunity and DTH in humans is unknown.

Immunity to Salmonella typhimurium infection in C3H/HeJ and C3H/HeNCrlBR mice: studies with an aromatic-dependent live S. typhimurium strain as a vaccine

Immunization with avirulent Salmonella typhimurium strain SL3235, a smooth, aroA- derivative, was shown to induce high levels of resistance to challenge with virulent S. typhimurium in innately hypersusceptible C3H/HeJ mice and inherently resistant C3H/HeNCrlBR mice. Strain SL3235 is one of a class of avirulent aroA- derivatives made from various strains and species of Salmonella that are being considered as vaccine candidates for cattle and humans. This paper supports their efficacy and potential utility in this regard. In C3H/HeJ mice, immunity against over 1,000 50% lethal doses of virulent S. typhimurium was evident as early as 3 days after immunization and persisted for at least 7 months. Further, the vaccine was effective over a broad spectrum of doses, ranging from 10(4) to 10(6) organisms. Infection with SL3235 led to marked splenomegaly in both mouse strains. The relationship of splenomegaly to the growth kinetics and colonization by SL3235 in the spleens of infected C3H/HeJ and C3H/HeNCrlBR mice was followed. SL3235 initially multiplied slowly in the spleens of both mouse strains and then was rapidly cleared. Less multiplication was seen in the resistant C3H/HeNCrlBR mice than in C3H/HeJ mice. Maximum splenomegaly occurred after clearance of the organism had begun. Protection against virulent S. typhimurium persisted after virtually all of the SL3235 vaccine strain had been cleared from the spleen. Cross-protection against Listeria monocytogenes was evident, but had a later onset, waned by 21 days, and was not detectable by 1 month after vaccination. Demonstration of this cross-protection is consistent with the interpretation that SL3235 induces cellular immunity. One-week immune spleen cells adoptively transferred anti-S. typhimurium and anti-L. monocytogenes immunity. T cell-enriched fractions were ineffective in adoptive transfer, as were spleen cells taken 2 weeks or later after immunization. Protective capacity was in the adherent cell fraction and seemed to be associated with macrophages. Evidence for induction of a population of sensitized T cells was obtained by using a peritoneal exudate T-lymphocyte proliferation assay on peritoneal T lymphocytes collected 1 to 3 months after SL3235 infection.

T-dependent production and activation of mononuclear phagocytes during murine BCG infection

Mice infected with a high dose of viable Bacillus Calmette Guerin (BCG) intravenously offer an interesting model to study regulatory functions of T cells on hemopoiesis. The proposition that T lymphocytes may play such a regulatory role was tested in nu/nu and two genetically different strains of mice: while the hemopoiesis of C3H/He mice remained unchanged during BCG injection, that of infected C57BL/6 mice was rapidly and transiently modified towards increased production of phagocytes at the expense of the erythroid lineage. The number of BCG-specific T cells present in C57BL/6 bone marrow was 50-100 higher than that determined in C3H/He mice. Moreover, between day 0 and 5 of infection the majority of BCG-specific T cells in C57BL/6 animals were of the L3T4+ Lyt2- surface phenotype. An attempt was made to identify the nature of the T cell product(s) able to activate young bone marrow-derived macrophages to render them non-permissive to growth of BCG.