Gamma Interferon Responses Induced by a Panel of Recombinant and Purified Mycobacterial Antigens in Healthy, Non-Mycobacterium bovisBCG-Vaccinated Malawian Young Adults

Abstract

We have previously shown that young adults living in a rural area of northern Malawi showed greater gamma interferon (IFN-␥) responses to purified protein derivatives (PPD) prepared from environmental mycobacteria than to PPD from Mycobacterium tuberculosis. In order to define the mycobacterial species to which individuals living in a rural African population have been exposed and sensitized, we tested T-cell recognition of recombinant and purified antigens from M. tuberculosis (38 kDa, MPT64, and ESAT-6), M. bovis There is great variation in the protection that Mycobacterium bovis BCG vaccines can provide against tuberculosis in different locations (17). In two large randomized controlled studies of BCG vaccination in Malawi and the United Kingdom, we have shown that prior to the vaccination of previously unvaccinated young adults in Malawi, over 60% of individuals show gamma interferon (IFN-␥) responses to purified protein derivative (PPD) from M. tuberculosis and that BCG vaccination provides only a moderate increase in this T-cell response (8). When PPDs from a number of nontuberculous environmental (atypical) mycobacteria were used to stimulate whole-blood cultures from the same subjects, PPDs from members of the M. avium-M. intracellulare-M. scrofulaceum complex induced stronger IFN-␥ responses than PPD from M. tuberculosis (6). To further define the mycobacterial species to which these subjects had been exposed, we have now used a panel of recombinant and purified antigens, with known species distributions, to test IFN-␥ responses, as a measure of the type 1 T-cell response induced by mycobacterial antigens, in day 6 supernatants from diluted whole-blood cultures. We have also assessed the potential of these recombinant antigens for identifying infection with M. tuberculosis and M. leprae, by studying the association between the IFN-␥ response to these antigens and the skin test response to M. tuberculosis PPD.Most studies of T-cell recognition of individual mycobacterial antigens have used patients infected with pathogenic mycobacteria or the contacts of these patients. Our study is unusual in that non-BCG-vaccinated, human immunodeficiency virus-negative, healthy individuals living in a rural area of northern Malawi have been tested for their ability to make a type 1 cytokine response to a panel of seven recombinant mycobacterial antigens and one purified native mycobacterial antigen. These subjects were clinically well at the time of testing and were recruited in their villages and homes.

Immunological consequences of intragenus conservation ofMycobacterium tuberculosisT-cell epitopes

“…For example, a population in Malawi with no history or scar evidence of prior bCG vaccination or MTB infection showed responsiveness to a variety of mycobacterial antigens and purified protein derivative (PPD) from different NTMs (5,6). In addition, non-MTB-infected and non-bCG-vaccinated individuals respond to MTB-encoded antigens, MTB lysate, and PPD (7,8).…”

Evaluation of T-Cell Responses to Novel RD1- and RD2-EncodedMycobacterium tuberculosisGene Products for Specific Detection of Human Tuberculosis Infection

“…Studies using several different assays, including lymphoproliferation, gamma interferon (IFN-␥) enzyme-linked immunosorbent assay (ELISA), and IFN-␥ enzyme-linked immunospot (ELISPOT) assay, have shown that they are strong targets of the cellular immune response in animal models, TB patients, and contacts (4,11,24,28,30,35,(37)(38)(39). However, we know very little about the remaining seven RD1 gene products.…”

Gamma Interferon-Based Immunodiagnosis of Tuberculosis: Comparison between Whole-Blood and Enzyme-Linked Immunospot Methods

“…A kit based on whole-blood production of IFN-␥ detected by enzyme-linked immunosorbent assay (ELISA) is available and has the advantage of relative simplicity, but being based on PPD, it does not ameliorate the poor specificity of skin testing (6). In addition, this test requires 10 ml of blood, a large amount if one considers its application in pediatric practice.We were interested to determine, by the use of a sensitive IFN-␥ ELISA, whether a form of the whole blood stimulation assay that is used by many groups to assay antigen specific responses to RD1 encoded antigens (1,3,7,9,16) could match the performance of the ELISPOT assay. Ethical permission for this study was provided by the Harrow local research ethics committee (Harrow LREC 1646).…”

“…We were interested to determine, by the use of a sensitive IFN-␥ ELISA, whether a form of the whole blood stimulation assay that is used by many groups to assay antigen specific responses to RD1 encoded antigens (1,3,7,9,16) could match the performance of the ELISPOT assay. Ethical permission for this study was provided by the Harrow local research ethics committee (Harrow LREC 1646).…”