Mycobacterium bovis BCG scar status and HLA class II alleles influence purified protein derivative-specific T-cell receptor V beta expression in pulmonary tuberculosis patients from southern India

Abstract

Purified protein derivative (PPD) RT23-recalled T-cell receptor (TCR) V beta expression was studied in the peripheral blood of 42 pulmonary tuberculosis patients and 44 healthy controls from southern India, a region where tuberculosis is endemic. Forty-eight-hour whole-blood cultures in the presence or absence of PPD-RT23 were set up, and at the end of the culture period total RNA was extracted and cDNA was synthesized. Expression of various TCR V beta families was assessed by using family-specific primers. PPD-specific expression (usage) of TCR V beta families 4, 6, 8 to 12, and 14 was found in more controls than patients. Among the responders (individuals who showed PPD-specific expression), endemic controls had significantly higher responses than the patients had for TCR V beta families 2, 3, 7, 13, and 17. The majority of the patients did not show usage of most of the TCR V beta families, and this was attributed to T-cell downregulation. A four-way nested classification analysis revealed that TCR V beta family 1, 5, 9, 12, and 13 usage in the context of HLA class II high-risk alleles (DRB1*1501, DRB1*08, and DQB1*0601) and Mycobacterium bovis BCG scar status were the determining factors in susceptibility and resistance to tuberculosis. The healthier status of controls was attributed to the wider usage of many TCR V beta families readily recalled by PPD, while the disease status of the patients was attributed to TCR V beta downregulation and the resultant T-cell (memory cell?) unresponsiveness. Host genetics (HLA status) and BCG vaccination (scar status) seem to play important roles in skewing the immune response in adult susceptibility to pulmonary tuberculosis through TCR V beta usage.

FIG. 1.

Agarose gels showing expression of various TCR Vβ families in PHA- or PPD-stimulated, 48-h whole-blood cultures from a healthy control. M, marker φX-HaeIII.

FIG. 2.

Concordance of repeat assays of TCR Vβ expression in response to PHA in two different individuals (A and B). Whole-blood cultures were set up in quadruplicate with 0.4 μg of PHA and harvested after 48 h by pooling two wells. RNAs were extracted, cDNAs were synthesized from both aliquots and pooled, and PCRs for TCR Vβ families were performed by using TCR Vβ family-specific primers twice on different days. The net intensities for the repeat experiments (in pixels) are compared. The numbers near the data points indicate TCR Vβ families. The regression line, 95% confidence interval, and prediction interval are indicated. C, TCR constant region.

FIG. 3.

TCR Vβ responders in healthy controls and pulmonary tuberculosis patients. The data indicate the percentage of responders in each TCR Vβ family. (A) No-antigen control; (B) antigen-specific usage. P values were obtained based on a chi-square analysis with the Yates correction.