India International Center for Excellence in Research

National Institute Of Allergy And Infectious Diseases

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Abstract

In the past year, we have completed a number of studies on the pathogenesis of Strongyloidiasis and the immunology of tuberculosis. We are also continuing our studies on TB - helminth co-infection and immune responses in TB and TB-diabetes. Strongyloidiasis pathogenesis: A. Role of Th1, Th2 and Th17 cells: Chronic helminth infections are known to be associated with modulation of antigen - specific CD4+ T responses. However, the role of CD4+ T cell responses in human infection with Strongyloides stercoralis (Ss) is not well-defined. To examine the role of CD4+ T cells expressing Th1, Th2 and Th17 cytokines in strongyloidiasis, we compared the frequency of these subsets in infected individuals (INF) to frequencies (Fo) in Ss-uninfected (UN) individuals. INF individuals exhibited a significant decrease in the spontaneous and antigen specific Fo of both mono - and dual functional Th1 cells compared to UN. Similarly, INF individuals also exhibited significantly decreased Fo of mono - and dual - functional Th17 cells upon antigen - stimulation compared to UN. In contrast, both the spontaneous and antigen - induced Fo of mono- and dual - functional Th2 cells was significantly increased in INF compared to UN individuals. This differential T cell response was predominantly antigen - specific since it was abrogated upon control antigen or mitogen stimulation. The regulation of Th1, Th2 and Th17 cells was pre-dominantly dependent on IL-10, while the regulation of Th2 but not Th1 or Th17 cells was also dependent on TGFb. In addition, treatment of Ss infection significantly increased the antigen - specific Fo of Th1 and Th17 cells and decreased the Fo of Th2 cells in INF individuals. Thus, Ss infection is characterized by an IL-10 dependent regulation of mono- and dual - functional Th1, Th2 and Th17 cells, a regulation also reversible by anti-helminthic treatment. B. Role of Th9 cells: Th9 cells are known to exert protective immunity in animal models of intestinal helminth infections. To examine the role of Th9 cells in Strongyloidis stercoralis (Ss), a common intestinal helminth infection, we compared the frequency of Th9 expressing IL-9 either singly (mono-functional) or co-expressing IL-4 or IL-10 (dual-functional) in Ss infected individuals (INF) to frequencies in uninfected (UN) individuals. INF individuals exhibited a significant increase in the spontaneously expressed and/or antigen specific frequencies of both mono - and dual functional Th9 cells as well as Th2 cells expressing IL-9 compared to UN. The differences in Th9 induction between INF and UN individuals was predominantly antigen - specific since it was abrogated upon control antigen or mitogen stimulation. In addition, the increased frequency of Th9 cells in response to parasite antigens was dependent on IL-10 and TGFb since neutralization of both these cytokines resulted in diminished Th9 frequencies. Finally, treatment of Ss infection also significantly decreased the antigen - specific frequencies of Th9 cells in INF individuals, suggesting a role for active infection in the Th9 response. Thus, Ss infection is characterized by an IL-10 and TGFb dependent expansion of Th9 cells, an expansion found to reversible by anti-helminthic treatment. Helminth and tuberculosis studies: A. Role of T cells in helminth - TB coinfection: 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-α and 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 immune activation: 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 their endogenous 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, matrix metalloproteinases, tissue inhibitors of matrix metalloproteinases as well as the systemic immune activation markers, sCD14 and sCD163. These changes are specific to ATB since they are absent in NTB individuals 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: Since Th1, Th2 and Th17 responses are known to play an important role in immunity to LTB, we postulated that coincident DM could alter the function of these CD4+ T cell subsets. To identify the role of Th1, Th2 and Th17 cells in LTB with coincident DM, we examined mycobacteriaspecific immune responses in the whole blood of individuals with LTB-DM and compared them with those without DM (LTB-NDM). LTB-DM is characterized by diminished frequencies of mono and dual functional CD4+ Th1, Th2 and Th17 cells at baseline and/or following mycobacterial - antigen stimulation. Finally, this modulation was at least partially dependent on the regulatory cytokines - IL-10 and TGFb since neutralization of either cytokine resulted in significantly increased frequencies of Th1 and Th2 cells but not Th17 cells. LTB-DM is therefore characterized by diminished frequencies of Th1, Th2 and Th17 cells, indicating that DM alters the immune response in latent TB leading to a defective induction of protective CD4+ T cell responses, thereby providing a potential mechanism for increased susceptibility to active disease.