Cell-mediated immunity is a key weapon of host defence
against tuberculosis (TB). Granzyme A (GzmA),
a serine protease, present in the granules of cytotoxic
cells induces caspase-independent cell death. We estimated
the proportion of GzmA producing lymphocyte
subsets in peripheral blood from 59 normal healthy
volunteers and 48 pulmonary TB (PTB) patients using
flow cytometry. When compared with normal healthy
subjects, we observed a significantly higher percentage
of GzmA-positive CD56+ cells (P = 0.01) in PTB
patients. However, when the absolute number was
compared between the two groups, a significantly decreased
number of GzmA-expressing CD16+ (P = 0.01)
and CD56+ (P = 0.0001) cells was observed in patients
and this could be explained by the significantly reduced
number of total lymphocytes (P = 0.0009) seen
in the patients. There was no significant difference in
the number of CD4+ and CD8+ GzmA double-positive
cells between the two study groups. CD56 is a natural
killer cell marker and these cells represent innate immune
response to TB. We report an increased percentage of
CD56+ cells expressing GzmA in TB patients, which
shows the relevance of the GzmA-mediated pathway
of apoptosis in immunity against Mycobacterium tuberculosis