Efficacy of oral and parenteral routes of Mycobacterium bovis bacille Calmette-Guerin vaccination against experimental bovine tuberculosis in white-tailed deer (Odocoileus virginianus): a feasibility study

We investigated the efficacy of oral and parenteral Mycobacterium bovis bacille Calmette-Guerin Danish strain 1331 (BCG) in its ability to protect white-tailed deer (Odocoileus virginianus) against disease caused by M. bovis infection. Twenty-two white-tailed deer were divided into four groups. One group (n=5) received 10(9) colony-forming units (cfu) BCG via a lipid-formulated oral bait; one group (n=5) received 10(9) cfu BCG in culture directly to the oropharynx, one group (n=6) was vaccinated with 10(6) cfu BCG subcutaneously, and one group served as a control and received culture media directly to the oropharynx (n=6). All animals were challenged 3 mo after vaccination. Five months postchallenge the animals were examined for lesions. Results indicate that both oral forms of BCG and parenterally administered BCG offered significant protection against M. bovis challenge as compared to controls. This study suggests that oral BCG vaccination may be a feasible means of controlling bovine tuberculosis in wild white-tailed deer populations.     

Naive helper T cells from BCG-vaccinated volunteers produce IFN-gamma and IL-5 to mycobacterial antigen-pulsed dendritic cells

Mycobacterium bovis bacillus Calmette-Guérin (BCG) is a live vaccine that has been used in routine vaccination against tuberculosis for nearly 80 years. However, its efficacy is controversial. The failure of BCG vaccination may be at least partially explained by the induction of poor or inappropriate host responses. Dendritic cells (DCs) are likely to play a key role in the induction of immune response to mycobacteria by polarizing the reactivity of T lymphocytes toward a Th1 profile, contributing to the generation of protective cellular immunity against mycobacteria. In this study we aimed to investigate the production of Th1 and Th2 cytokines by naive CD4+ T cells to mycobacterial antigen-pulsed DCs in the group of young, healthy BCG vaccinated volunteers. The response of naive helper T cells was compared with the response of total blood lymphocytes. Our present results clearly showed that circulating naive CD45RA+CD4+ lymphocytes from BCG-vaccinated subjects can become effector helper cells producing IFN-gamma and IL-5 under the stimulation by autologous dendritic cells presenting mycobacterial protein antigen-PPD or infected with live M. bovis BCG bacilli.     

A combined DNA vaccine-prime, BCG-boost strategy results in better protection against Mycobacterium bovis challenge

In this study, we demonstrated that calves vaccinated with a combined DNA vaccine encoding Ag85B, MPT- 64, and MPT-83 antigens from the Mycobacterium tuberculosis for the priming and subsequently boosting with BCG prior to experimental challenge with virulent Mycobacterium bovis (M. bovis) resulted in improved immune responses over immunizing. Vaccination with the combined DNA/BCG induced higher levels of antigen- specific gamma interferon (IFN-gamma) in whole-blood cultures 4 weeks after final vaccination and the level of antigen-specific IFN-gamma in response to Ag85, MPT-64, and MPT-83 were still higher 4 weeks after challenge when compared to the combined DNA group. There was a significant bias toward induction of CD4+ T cells rather than CD8+ T cells responses, and the mean percentage of CD4+ T cells was increased about 2.6-fold in peripheral blood mononuclear cells (PBMC) cultures in DNA prime-BCG boost vaccination when compared to the nonvaccinated group. In addition, DNA prime-BCG boost vaccination resulted in stronger humoral immune responses, and the levels of the specific antibodies to three antigens were increased two- to 32- fold when compared to the combined DNA group. Vaccination with the combined DNA/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 to the nonvaccinated group. Finally, the combined DNA/BCG increased the protective efficacy by more than 10-100-fold as measured by reduced CFU counts in the lungs from calves challenged with M. bovis compared to the combined DNA and BCG groups. These results suggest that use of the prime-boost strategy offers better protection against bovine tuberculosis than does the combined DNA vaccines and BCG.     

Lymphatic tracing and T cell responses following oral vaccination with live Mycobacterium bovis (BCG)

Oral vaccination of mice with lipid-encapsulated Mycobacterium bovis bacille Calmette-Guérin (BCG) expands a subset of interferon-gamma (IFN-gamma)-secreting T cells and mediates protection against aerosol mycobacterial challenge. We have traced the movement of the live vaccine through the regional lymphatics of mice and monitored the resultant immune response. Six hours after oral vaccination BCG was detected in low numbers systemically and in draining lymphatic tissue. However, after 48 h, BCG was predominantly associated with alimentary tract lymphatic tissues, such as the cervical and mesenteric lymph nodes and Peyer's patches. Lymphocytes that produced IFN-gamma in response to PPD-B or BCG-pulsed dendritic cells predominated in the spleen and were almost exclusively CD4(+), CD44(+) and CD62L(-), thus resembling an effector memory T cell population. Despite the fact that an oral route was used for immunization, splenic IFN-gamma-secreting T cells in vaccinated mice did not express the mucosal homing antigens alpha(4)beta(7) integrin or alphaIEL (CD103). However, a proportion of BCG-specific CD4(+) T cells expressed the CD29 integrin (beta(1)) chain, potentially involved in lung homing function. Thus, oral priming with M. bovis BCG appears to induce a subset of spleen-resident CD4(+) T cells with the potential to provide protective immunity in the lung.     

Specificity of antigenic fractions of tuberculin.

Purified protein derivative from Mycobacterium bovis was separated into 6 fractions by electrophoresis at 1500 V/40 mA in pH 4.2 acetic acid-pyridine buffer. Further purification of one of the fractions on Sephadex G 25 column and by acid hydrolysis yielded antigen "PS" eliciting tuberculin reaction only in animals vaccinated with M. bovis BCG but not in those sensitized with M. avium and some fast-growing mycobacteria. The specificity of antigen "PS" was confirmed in vitro: the antigen induced blastic transformation only in lymphocytes of guinea pigs sensitized with M. bovis BCG.     

Nitric oxide production as an indication of Mycobacterium bovis infection in white-tailed deer (Odocoileus virginianus)

White-tailed deer (Odocoileus virginianus) are reservoirs for Mycobacterium bovis in northeast Michigan, USA. Production of nitric oxide (NO) by activated macrophages is a potent mechanism of mycobacterial killing. The capacity of macrophages to produce NO, however, varies among mammalian species. The objective of this study was to determine if mononuclear cells from white-tailed deer produce nitrite as an indication of NO production and, if so, is NO produced in response to stimulation with M. bovis antigens. Supernatants were harvested from adherent peripheral blood mononuclear cell (PBMC) cultures that had been stimulated with either Mannheimia haemolytica lipopolysaccharide (LPS) or media alone (i.e., no stimulation). Nitrite levels within M. haemolytica LPS-stimulated culture supernatants exceeded (P < 0.05) those detected within supernatants from non-stimulated cultures as well as those detected within supernatants from cultures receiving an inhibitor of NO synthase in addition to M. haemolytica LPS. In response to stimulation with M. bovis antigens, nitrite production by PBMC from M. bovis-infected deer exceeded (P < 0.05) the production by PBMC from non-infected deer. The response of PBMC from infected deer to M. bovis antigens exceeded (P < 0.05) the response of parallel cultures from the same deer receiving no stimulation. The response of PBMC from M. bovis-infected deer to M. avium antigens did not differ from that of PBMC from M. bovis-infected deer to no stimulation or from that of PBMC from non-infected deer to M. avium antigens. These findings indicate that adherent PBMC from white-tailed deer are capable of NO production and that mononuclear cells isolated from M. bovis-infected white-tailed deer produce NO in an antigen-specific recall response.     

Protection against tuberculosis in Eurasian wild boar vaccinated with heat-inactivated Mycobacterium bovis

Tuberculosis (TB) caused by Mycobacterium bovis and closely related members of the Mycobacterium tuberculosis complex continues to affect humans and animals worldwide and its control requires vaccination of wildlife reservoir species such as Eurasian wild boar (Sus scrofa). Vaccination efforts for TB control in wildlife have been based primarily on oral live BCG formulations. However, this is the first report of the use of oral inactivated vaccines for controlling TB in wildlife. In this study, four groups of 5 wild boar each were vaccinated with inactivated M. bovis by the oral and intramuscular routes, vaccinated with oral BCG or left unvaccinated as controls. All groups were later challenged with a field strain of M. bovis. The results of the IFN-gamma response, serum antibody levels, M. bovis culture, TB lesion scores, and the expression of C3 and MUT genes were compared between these four groups. The results suggested that vaccination with heat-inactivated M. bovis or BCG protect wild boar from TB. These results also encouraged testing combinations of BCG and inactivated M. bovis to vaccinate wild boar against TB. Vaccine formulations using heat-inactivated M. bovis for TB control in wildlife would have the advantage of being environmentally safe and more stable under field conditions when compared to live BCG vaccines. The antibody response and MUT expression levels can help differentiating between vaccinated and infected wild boar and as correlates of protective response in vaccinated animals. These results suggest that vaccine studies in free-living wild boar are now possible to reveal the full potential of protecting against TB using oral M. bovis inactivated and BCG vaccines.     

Bacillus Calmette-Guérin vaccination of human newborns induces T cells with complex cytokine and phenotypic profiles

The immune response to vaccination with bacillus Calmette-Guérin (BCG), the only tuberculosis vaccine available, has not been fully characterized. We used multiparameter flow cytometry to examine specific T cell cytokine production and phenotypic profiles in blood from 10-wk-old infants routinely vaccinated with BCG at birth. Ex vivo stimulation of whole blood with BCG for 12 h induced expression of predominantly IFN-gamma, IL-2, and TNF-alpha in CD4+ T cells in seven distinct cytokine combinations. IL-4 and IL-10 expression was detected in CD4+ T cells at low frequencies and only in cells that did not coexpress type 1 cytokines. Specific CD8+ T cells were less frequent than CD4+ T cells and produced mainly IFN-gamma and/or IL-2 and less TNF-alpha, IL-4, and IL-10. Importantly, many mycobacteria-specific CD4+ and CD8+ T cells did not produce IFN-gamma. The predominant phenotype of BCG-specific type 1 T cells was that of effector cells, i.e., CD45RA-CCR7-CD27+, which may reflect persistence of Mycobacterium bovis BCG in infants until 10 wk of age. Among five phenotypic patterns of CD4+ T cells, central memory cells were more likely to be IL-2+ and effector cells were more likely to be IFN-gamma+. We concluded that neonatal vaccination with BCG induces T cells with a complex pattern of cytokine expression and phenotypes. Measuring IFN-gamma production alone underestimates the magnitude and complexity of the host cytokine response to BCG vaccination and may not be an optimal readout in studies of BCG and novel tuberculosis vaccination.     

The Potential for Transmission of BCG from Orally Vaccinated White-Tailed Deer (Odocoileus virginianus) to Cattle (Bos taurus) through a Contaminated Environment: Experimental Findings

White-tailed deer (Odocoileus virginianus) experimentally infected with a virulent strain of Mycobacterium bovis have been shown to transmit the bacterium to other deer and cattle (Bos taurus) by sharing of pen waste and feed. The risk of transmission of M. bovis bacille Calmette-Guerin (BCG) vaccine from orally vaccinated white-tailed deer to other deer and cattle, however, is not well understood. In order to evaluate this risk, we orally vaccinated 14 white-tailed deer with 1×10⁹ colony forming units BCG in lipid-formulated baits and housed them with nine non-vaccinated deer. Each day we exposed the same seven naïve cattle to pen space utilized by the deer to look for transmission between the two species. Before vaccination and every 60 days until the end of the study, we performed tuberculin skin testing on deer and cattle, as well as interferon-gamma testing in cattle, to detect cellular immune response to BCG exposure. At approximately 27 weeks all cattle and deer were euthanized and necropsied. None of the cattle converted on either caudal fold, comparative cervical tests, or interferon-gamma assay. None of the cattle were culture positive for BCG. Although there was immunological evidence that BCG transmission occurred from deer to deer, we were unable to detect immunological or microbiological evidence of transmission to cattle. This study suggests that the risk is likely to be low that BCG-vaccinated white-tailed deer would cause domestic cattle to react to the tuberculin skin test or interferon-gamma test through exposure to a BCG-contaminated environment.     

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.     

Oral Vaccination of White-Tailed Deer (Odocoileus virginianus) with Mycobacterium bovis Bacillus Calmette-Guerin (BCG)

Wildlife reservoirs of Mycobacterium bovis represent serious obstacles to the eradication of tuberculosis from livestock, particularly cattle. In Michigan, USA tuberculous white-tailed deer transmit M. bovis to other deer and cattle. One approach in dealing with this wildlife reservoir is to vaccinate deer, thus interfering with the intraspecies and interspecies transmission cycles. Thirty-three white-tailed deer were assigned to one of two groups; oral vaccination with 1×10⁸ colony-forming units of M. bovis BCG Danish (n = 17); and non-vaccinated (n = 16). One hundred eleven days after vaccination deer were infected intratonsilarly with 300 colony-forming units of virulent M. bovis. At examination, 150 days after challenge, BCG vaccinated deer had fewer gross and microscopic lesions, fewer tissues from which M. bovis could be isolated, and fewer late stage granulomas with extensive liquefactive necrosis. Fewer lesions, especially those of a highly necrotic nature should decrease the potential for dissemination of M. bovis within the host and transmission to other susceptible hosts.     

Cytolytic T-cell responses to human dendritic cells and macrophages infected with Mycobacterium bovis BCG and recombinant BCG secreting listeriolysin

Cytolytic T-cell responses from 63 normal blood donors were monitored in a Mycobacterium bovis BCG infection system in vitro. We wanted to know whether cultured dendritic cells were capable of potentiating the cytolytic T-cell responses to M. bovis BCG. Infected cultured dendritic cells were up to ten times more effective antigen-presenting cells than macrophages in proliferative assays, while cytolytic T-cell induction did not differ significantly between dendritic cells and macrophages. Separated CD4+ and CD8+ T-cell subsets contributed equally to lysis of infected targets. Experiments comparing wild-type M. bovis BCG strain with two new recombinant M. bovis BCG strains secreting listeriolysin revealed statistically significant higher maximal lysis values for recombinant M. bovis BCG. We conclude from our in vitro infection system with mycobacteria that dendritic cells are superior to macrophages in proliferative assays but equal to macrophages in their ability to induce cytolytic T-cell responses. Moreover, our data suggest that recombinant M. bovis BCG vaccine strains secreting listeriolysin improve cytolytic T-cell responses.     

Regulation of Mycobacterium-specific mononuclear cell responses by 25-hydroxyvitamin D3

The active vitamin D metabolite, 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), has been shown to be an important regulator of innate and adaptive immune function. In addition, synthesis of 1,25(OH)(2)D(3) from 25-hydroxyvitamin D(3) (25(OH)D(3)) by the enzyme 1α-hydroxylase in monocytes upon activation by TLR signaling has been found to regulate innate immune responses of monocytes in an intracrine fashion. In this study we wanted to determine what cells expressed 1α-hydroxylase in stimulated peripheral blood mononuclear cell (PBMC) cultures and if conversion of 25(OH)D(3) to 1,25(OH)(2)D(3) in PBMC cultures regulated antigen-specific immune responses. Initially, we found that stimulation of PBMCs from animals vaccinated with Mycobacterium bovis (M. bovis) BCG with purified protein derivative of M. bovis (M. bovis PPD) induced 1α-hydroxylase gene expression and that treatment with a physiological concentration of 25(OH)D(3) down-regulated IFN-γ and IL-17F gene expression. Next, we stimulated PBMCs from M. bovis BCG-vaccinated and non-vaccinated cattle with M. bovis PPD and sorted them by FACS according to surface markers for monocytes/macrophages (CD14), B cells (IgM), and T cells (CD3). Sorting the PBMCs revealed that 1α-hydroxylase expression was induced in the monocytes and B cells, but not in the T cells. Furthermore, treatment of stimulated PBMCs with 25(OH)D(3) down-regulated antigen-specific IFN-γ and IL-17F responses in the T cells, even though 1α-hydroxylase expression was not induced in the T cells. Based on evidence of no T cell 1α-hydroxylase we hypothesize that activated monocytes and B cells synthesize 1,25(OH)(2)D(3) and that 1,25(OH)(2)D(3) down-regulates antigen-specific expression of IFN-γ and IL-17F in T cells in a paracrine fashion.     

Manipulation of immune responses to Mycobacterium bovis by vaccination with IL-2- and IL-18-secreting recombinant bacillus Calmette Guerin

Bacillus Calmette Guerin (BCG) has been reported to show variable efficacy as a vaccine against tuberculosis. We demonstrated that the secretion of biologically active IL-2 (rBCG/IL-2),but not IL-18 (rBCG/IL-18), by BCG improves its ability to induce and maintain a strong type 1 immune response in BALB/c mice. rBCG/IL-2 induced significantly higher Ag-specific proliferative responses, high IFN-gamma production and serum titres of IgG2a 16 weeks after vaccination. This immune profile was correlated to an increased rate of clearance of non-pathogenic mycobacteria (live BCG delivered intranasally). Surprisingly, however,this strong type 1 immune profile induced no greater protective immunity against aerosol challenge with virulent Mycobacterium bovis than that induced by normal BCG (nBCG). By comparison,vaccination with rBCG/IL-18 was found to induce significantly less IFN-gamma production in splenic lymphocytes than nBCG.This impaired induction of IFN-gamma was correlated to a significantly lower protective efficacy against M. bovis challenge, as compared to nBCG. The data suggest that manipulation of the immune response to tuberculosis and tuberculosis vaccines will require a more complete understanding of the factors that are important in generating a protective immune response.     

Characterization of a Mycobacterium bovis BCG insertion sequence related to the IS21 family

The structure and distribution of a Mycobacterium bovis BCG insertion element of the IS21 family were investigated. Several IS21-like elements found in mycobacterial genomes were separated in four types, following their nucleic acid similarities. The M. bovis BCG IS21 element is highly similar to IS1533 (class I), 70% similar to IS1534 (class II), 52% similar to IS1532 (class III) of Mycobacterium tuberculosis, and 54% similar to both an Mycobacterium avium serovar 2 and an M. avium silvaticum IS (class IV). The M. bovis BCG IS21 element of the class I appears to be present in a single copy in the genome of M. bovis BCG, M. bovis, M. tuberculosis and Mycobacterium africanum and to be absent from all other tested species of the Corynebacteria-Mycobacteria-Nocardia group.     

Screening and Assessing 11 Mycobacterium tuberculosis Proteins as Potential Serodiagnostical Markers for Discriminating TB Patients from BCG Vaccinees

Purified protein derivative (PPD) skin tests often yield poor specificity, so that to develop new serological antigens for distinguishing between Mycobacterium tuberculosis infection and Bacille Calmette-Guerin (BCG) vaccination is a priority, especially for developing countries like China. We predicted the antigenicity for selected open reading frames (ORFs) based on the genome sequences of M. tuberculosis H37Rv and M. bovis BCG, as well as their functions and differences of expression under different stim...     

Survival of Mycobacterium bovis on feedstuffs commonly used as supplemental feed for white-tailed deer (Odocoileus virginianus)

Mycobacterium bovis, the causative agent of bovine tuberculosis, has become established in free-ranging white-tailed deer Odocoileus virginianus in northeastern Michigan. The practice of supplemental feeding of white-tailed deer during the winter is believed to contribute to transmission of M. bovis between deer. The current study was conducted to determine the ability of M. bovis to survive on various feedstuffs commonly used as supplemental feed for deer in northeast Michigan (i.e., apples, corn, carrots, sugar beets, potatoes, and hay) and the effect of maintenance at -20 C, 8 C, and 23 C on survival. Mycobacterium bovis survived on all feedstuffs at all temperatures tested for at least 7 days. At 23 C, M. bovis could still be isolated from samples of apples, corn and potatoes at 112 days. This study suggests that contamination of feedstuffs by M. bovis-infected deer could act as a source of indirect transmission between deer because M. bovis is able to survive in temperatures similar to those recorded during winter months in northeastern Michigan. Current efforts to ban or control supplemental feeding of deer should have a positive effect on decreasing transmission of M. bovis among deer.     

BCG induces protection against Mycobacterium tuberculosis infection in the Wistar rat model

Our understanding of the correlation of Mycobacterium bovis Bacille Calmette-Guerin (BCG)-mediated immune responses and protection against Mycobacterium tuberculosis (Mtb) infection is still limited. We have recently characterized a Wistar rat model of experimental tuberculosis (TB). In the present study, we evaluated the efficacy of BCG vaccination in this model. Upon Mtb challenge, BCG vaccinated rats controlled growth of the bacilli earlier than unvaccinated rats. Histopathology analysis of infected lungs demonstrated a reduced number of granulomatous lesions and lower parenchymal inflammation in vaccinated animals. Vaccine-mediated protection correlated with the rapid accumulation of antigen specific CD4(+) and CD8(+) T cells in the infected lungs. Immunohistochemistry further revealed higher number of CD8(+) cells in the pulmonary granulomas of vaccinated animals. Evaluation of pulmonary immune responses in vaccinated and Mtb infected rats by real time PCR at day 15 post-challenge showed reduced expression of genes responsible for negative regulation of Th1 immune responses. Thus, early protection observed in BCG vaccinated rats correlated with a similarly timed shift of immunity towards the Th1 type response. Our data support the importance of (i) the Th1-Th2 balance in the control of mycobacterial infection and (ii) the value of the Wistar rats in understanding the biology of TB.     

Mycobacterium bovis bacille Calmette-Guérin infection in the CNS suppresses experimental autoimmune encephalomyelitis and Th17 responses in an IFN-gamma-independent manner

Multiple sclerosis and an animal model resembling multiple sclerosis, experimental autoimmune encephalomyelitis (EAE), are inflammatory demyelinating diseases of the CNS that are suppressed by systemic mycobacterial infection in mice and BCG vaccination in humans. Host defense responses against Mycobacterium in mice are influenced by T lymphocytes and their cytokine products, particularly IFN-gamma, which plays a protective regulatory role in EAE. To analyze the counter-regulatory role of mycobacterial infection-induced IFN-gamma in the CNS on the function of the pathological Th17 cells and the clinical outcome of EAE, we induced EAE in mice that were intracerebrally infected with Mycobacterium bovis bacille Calmette-Guerin (BCG). In this study, we demonstrate that intracerebral (i.c.) BCG infection prevented inflammatory cell recruitment to the spinal cord and suppressed the development of EAE. Concomitantly, there was a significant decrease in the frequency of myelin oligodendrocyte glycoprotein-specific IFN-gamma-producing CD4(+) T cells in the CNS. IL-17(+)CD4(+) T cell responses were significantly suppressed in i.c. BCG-infected mice following EAE induction regardless of T cell specificity. The frequency of Foxp3(+)CD4(+) T cells in these mice was equivalent to that of control mice. Intracerebral BCG infection-induced protection of EAE and suppression of myelin oligodendrocyte glycoprotein-specific IL-17(+)CD4(+) T cell responses were similar in both wild-type and IFN-gamma-deficient mice. These data show that live BCG infection in the brain suppresses CNS autoimmunity. These findings also reveal that the regulation of Th17-mediated autoimmunity in the CNS can be independent of IFN-gamma-mediated mechanisms.