Abstract
BackgroundIn vivo kinetics and frequencies of epitope-specific CD4 T cells in lymphoid compartments during M. tuberculosis infection and their resting memory pool after BCG vaccination remain unknown.Methodology/FindingsMacaque DR*W201 tetramer loaded with Ag85B peptide 65 was developed to directly measure epitope-specific CD4 T cells in blood and tissues form macaques after M. tuberculosis infection or BCG vaccination via direct staining and tetramer-enriched approach. The tetramer-based enrichment approach showed that P65 epitope-specific CD4 T cells emerged at mean frequencies of ∼500 and ∼4500 per 107 PBL at days 28 and 42, respectively, and at day 63 increased further to ∼22,000/107 PBL after M. tuberculosis infection. Direct tetramer staining showed that the tetramer-bound P65-specific T cells constituted about 0.2–0.3% of CD4 T cells in PBL, lymph nodes, spleens, and lungs at day 63 post-infection. 10-fold expansion of these tetramer-bound epitope-specific CD4 T cells was seen after the P65 peptide stimulation of PBL and tissue lymphocytes. The tetramer-based enrichment approach detected BCG-elicited resting memory P65-specific CD4 T cells at a mean frequency of 2,700 per 107 PBL.SignificanceOur work represents the first elucidation of in vivo kinetics and frequencies for tetramer-bound epitope-specific CD4 T cells in the blood, lymphoid tissues and lungs over times after M. tuberculosis infection, and BCG immunization.
Highlights
CD4 T cells play a critical role in immune protection
We evaluated standard tetramer direct staining, tetramer staining after peptide stimulation, and tetramer-based enrichment approaches for direct measurements of epitope-specific CD4 T cells in blood, lungs, lymph nodes and spleens during M. tuberculosis infection of Mamu-DRB*W201+ rhesus macaques
We identified that the class II MHC gene encoding Mamu-DRB*W201 allele as designated in the nonhuman primate data base was shared by the four Bacillus Calmette-Guerin (BCG)-vaccinated macaques that developed proliferative responses to peptide 65 (P65)
Summary
CD4 T cells play a critical role in immune protection. CD4 T cells function through their capacity to help B cells produce antibodies, to activate macrophages for enhanced microbicidal activity, to recruit leukocytes to infection/inflammation sites, and through their production of cytokines and chemokines to orchestrate adaptive immune responses. Direct tracking of class II MHC-restricted epitope-specific CD4 T cells will help to elucidate evolution or differentiation of Th1, Th2, Th17 and Treg cell populations in development of balanced antimicrobial immunity against viral or bacterial infections. Given the possibility that human Th1, Th2, Th17 and Treg cells play a role in immune regulation of tuberculosis, it is important to determine the evolution and interrelation of these CD4 T cell populations in primary M. tuberculosis infection. Developing better assay systems for direct measurement of MHC-restricted epitope-specific CD4 T cells should be an important step toward in-depth studies of evolution and immune function of Th1, Th2, Th17 and Treg during primary M. tuberculosis infection. In vivo kinetics and frequencies of epitope-specific CD4 T cells in lymphoid compartments during M. tuberculosis infection and their resting memory pool after BCG vaccination remain unknown
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