Tuberculin Skin Test Reactivity, Absence Of

For background information on susceptibility and resistance to Mycobacterium tuberculosis, see 607948.

Description

The tuberculin skin test (TST), or Mantoux test, measures induration of the skin after intradermal inoculation of M. tuberculosis purified protein derivative and thereby detects M. tuberculosis-infected and -noninfected persons. The TST triggers a classical T cell-mediated delayed-type hypersensitivity reaction against mycobacterial antigens. About 20% of individuals living in areas hyperendemic for tuberculosis show persistent absence of TST reactivity, suggesting T cell-independent resistance to M. tuberculosis infection. Genetic epidemiologic studies in endemic areas have suggested that host genetic factors contribute to resistance to M. tuberculosis infection and to the immune reactions underlying TST reactivity (summary by Cobat et al., 2009).

Mapping

Cobat et al. (2009) performed genomewide linkage analysis for TST reactivity in 128 families, including 186 parents and 350 children, from a suburb of Cape Town, South Africa, hyperendemic for tuberculosis. They identified a locus for the absence of TST reactivity, which they called TST1, on chromosome 11p14 with a lod score of 3.81 at position 26.37 Mb (P = 1.4 x 10(-5)). Suggestive linkage for absence of TST reactivity was also observed at chromosome 5p15 (lod score = 2.39; P = 0.0005) at the same position as TST2 (613637), a quantitative trait locus for TST reactivity in millimeters. Cobat et al. (2009) proposed that TST1 represents a major locus for T cell-independent resistance to M. tuberculosis, since a substantial portion of individuals who exhibit absence of TST reactivity are most likely resistant to M. tuberculosis infection.