In the past year, we have completed a number of studies on the pathogenesis of lymphatic filariasis and the immunology of tuberculosis. We are also continuing our studies on TB - helminth co-infection and immune responses in TB and TB-diabetes. Lymphatic filariasis (LF) pathogenesis: A. Role of Th17 and Th22 cells: Lymphatic filarial disease is known to be associated with elevated Th1 and normal or diminished Th2 responses to parasite-specific antigens. The role of Th17 and the recently described Th22 cells has not been examined in detail in either filarial infection per se or in filarial disease (e.g. lymphedema and elephantiaisis). To explore the role of Th17 and Th22 cells and their subsets, we examined the frequency of these cells in individuals with filarial lymphedema (CP), in clinically asymptomatic, infected (INF) and in uninfected (UN) individuals ex vivo and in response to parasite and non-parasite antigens. Those with disease (CP) had a significantly expanded frequency of Th17 and Th22 cells compared to either INF or UN individuals at baseline (ex vivo) and in response to parasite Ag. This antigen driven expansion of Th17 and Th22 cells was dependent on IL-1, IL-23 and to lesser on extent on TGFb as blockade of any of these cytokines resulted in significantly diminished frequencies of Th17 and Th22 cells. Our findings, therefore, suggest that filarial parasite driven expansion of Th17 and Th22 cells is associated with the pathogenesis of filarial infection and disease. B. Role of CD8+ T cells: Lymphatic filariasis is known to be associated with diminished CD4+ Th1 and elevated CD4+ Th2 responses to parasite-specific antigens. The role of cytokine expressing CD8+ T cells in the immune response to filarial infection is not well defined. To study the role of CD8+ T cells expressing Type 1, 2 and 17 cytokines in filarial infection, we examined the frequency of these cells in clinically asymptomatic patently-infected individuals (INF) directly ex vivo and in response to parasite or non-parasite antigens;these frequencies were compared to those with filarial lymphedema (CP) and those without active infection or pathology (EN). INF individuals exhibited a significant decrease in the frequency of CD8+ T cells expressing TNF-a, IFNg and IL-22 at baseline and/or in response to filarial antigens compared to CP and EN individuals. In contrast, these same individuals exhibited a significant increase in the frequency of CD8+ T cells expressing IL-4, IL-5, IL-9, IL-13 and IL-21 in comparison to CP and/or EN individuals. In addition, curative treatment resulted in significantly increased frequencies of CD8+ T cells expressing IL-2 and significantly decreased frequencies of CD8+ T cells expressing Type 2 cytokines. Finally, the regulation of these responses appear to be independent of IL-10 and TGFb since blockade of IL-10 or TGFb signaling did not significantly alter the frequencies of Type 1 or Type 2 cytokine expressing CD8+ T cells. Thus, our findings suggest that alterations in the frequencies of cytokine expressing CD8+ T cells are a characteristic feature of lymphatic filarial infection. Helminth and tuberculosis studies: A. Role of CD4+ and CD8+ T cells: Tissue invasive helminth infections and tuberculosis (TB) are co endemic in many parts of the world and can trigger immune responses that might antagonize each other. We have previously shown that helminth infections modulate the Th1 and Th17 responses to mycobacterial - antigens in latent TB. To determine whether helminth infections modulate antigen - specific and non - specific immune responses in active pulmonary TB, we examined CD4+ and CD8+ T cell responses as well as the systemic (plasma) cytokine levels in individuals with pulmonary TB with or without two distinct helminth infections - Wuchereria bancrofti and Strongyloides stercoralis infection. By analyzing the frequencies of Th1 and Th17 CD4+ and CD8+ T cells and their component subsets (including multifunctional cells), we report a significant diminution in the mycobacterial specific frequencies of mono - and multi functional CD4+ Th1 and (to a lesser extent) Th17 cells when concomitant filarial or Strongyloides infection occurs. The impairment in CD4+ and CD8+ T cell cytokine responses was antigen - specific as polyclonal activated T cell frequencies were equivalent irrespective of helminth infection status. This diminution in T cell responses was also reflected in diminished circulating levels of Th1 (IFN-γ, TNF-αand IL-2)- and Th17 (IL-17A and IL-17F)-associated cytokines. Finally, we demonstrate that for the filarial co-infections at least, this diminished frequency of multifunctional CD4+ T cell responses was partially dependent on IL-10 as IL-10 blockade significantly increased the frequencies of CD4+ Th1 cells. Thus, co-existent helminth infection is associated with an IL-10 mediated (for filarial infection) profound inhibition of antigen - specific CD4+ T cell responses as well as protective systemic cytokine responses in active pulmonary TB. B. Role of innate factors: Helminth infections are known to modulate innate and adaptive immune responses in active and latent tuberculosis (TB). However, the role of helminth infections in modulating responses associated with inflammation and immune activation (reflecting disease activity and/or severity) in TB is not known. We measured markers of inflammation and immune activation in active pulmonary TB individuals (ATB) with co-incidental Strongyloides stercoralis (Ss) infection. These included systemic levels of acute phase proteins, matrix metalloproteinases and inhibitors and immune activation markers. As a control, we measured the systemic levels of the same molecules in TB-uninfected individuals (NTB) with or without Ss infection. Our data confirm that ATB is associated with elevated levels of the various measured molecules when compared to those seen in NTB. Our data also reveal that co-incident Ss infection in ATB individuals is associated with significantly decreased circulating levels of acute phase proteins, MMPs, TIMPs, as well as sCD14, sCD163 and HO-1. These changes are specific to ATB with Ss infection. Our data therefore reveal a profound effect of Ss infection on the markers associated with TB disease activity and severity and indicate that co-incidental helminth infections might dampen the severity of TB disease. Tuberculosis and Diabetes Studies: A. Influence of DM and pre-DM on latent TB: Type 2 diabetes mellitus (DM) is known to be a major risk factor for the development of active tuberculosis (TB), although its influence on latent TB (LTBI) remains poorly characterized. We examined circulating plasma cytokine levels in individuals with LTBI with diabetes or pre-diabetes and compared them to those with LTBI with normal glycemic control. LTBI with DM or pre-DM is characterized by diminished circulating levels of Type 1 (IFNg, IL-2 and TNF-a) and Type 17 (IL-17F) cytokines. This was associated with decreased systemic levels of other pro-inflammatory cytokines (IL-1a and IL-18) and the anti- inflammatory cytokine (IL-10) but not Type 2 cytokines. Moreover, LTBI-DM individuals had diminished levels of spontaneous and TB - antigen specific levels of Type 1 and Type 17 cytokines when antigen stimulated whole blood was examined. Finally, there was no significant correlation between any of the cytokines measured (with the exception of IL-22) with hemoglobin A1C (HbA1c) levels. Our data reveal LTBI in the presence of diabetes or pre-diabetes is characterized by diminished production of cytokines implicated in control of TB activation allowing for a potential immunological mechanism that could account for the increased risk of active TB in DM.
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