Human T-cell responses to secreted antigen fractions of Mycobacterium tuberculosis

The T-cell response of human donors to secreted antigen fractions of Mycobacterium tuberculosis was investigated. The donors were divided into five groups: active pulmonary tuberculosis (TB) patients with minimal and with advanced disease, Mycobacterium bovis BCG-vaccinated donors with and without contact with TB patients, and nonvaccinated individuals. We found that patients with active minimal TB responded powerfully to secreted antigens contained in a short-term culture filtrate. The response to secreted antigens was mediated by CD4+ Th-1-like lymphocytes, and the gamma interferon release by these cells was markedly higher in patients with active minimal TB than in healthy BCG-vaccinated donors. Patients with active advanced disease exhibited depressed responses to all preparations tested. The specificity of the response to secreted antigens was investigated by stimulating lymphocytes with narrow-molecular-mass fractions of short-term culture filtrate obtained by the multielution technique. Considerable heterogeneity was found within the donor groups. Patients with active minimal TB recognized multiple secreted targets, but interestingly, six of eight patients demonstrated a predominant recognition of a low-mass (< 10-kDa) protein fraction which induced high levels of gamma interferon release in vitro. Only a few of 12 previously characterized secreted antigens were recognized by T cells isolated from TB patients, suggesting the existence of a number of as yet undefined antigenic targets among secreted antigens.