Neutrophil or polymorphonuclear leukocytes are critical to host defense. They act by migrating (chemotaxis) to site of inflammation or infection, phagocytoze the microorganisms to form phagosome. Reactive Oxygen species and hydrolytic enzymes are released (respiratory burst activity) into this phagosome to kill ingested microorganisms (microbicidal activity). Thyroid hormones are essential for proper differentiation, growth and metabolism of an organism. Increasing evidence indicates that thyroid hormones also play an active role in immunity. Subclinical hypothyroidism is associated with normal thyroid hormone levels with increased thyroid stimulating hormone level. While studies indicate elevated TSH to have some effects on immune functions, there is very little evidence regarding its effect on functional features of neutrophils. In this cross-sectional comparative study, we evaluated the phagocytic, chemotactic, candidacidal, and respiratory burst activity of neutrophils in subclinical hypothyroid and euthyroid subjects. Phagocytosis and metabolic function of the neutrophils was assessed using Nitro-blue tetrazolium test. Chemotaxis, directional movement of the PMNs was measured using the N-Formyl methionyl-leucyl-phenylalanine as chemoattractant. Phagocytic activity was evaluated by exposing leukocytes to candida suspension and counting the number of candida ingested and killed. Microbicidal activity of neutrophils was assessed by the ability of leukocytes to kill Candida albicans in both subclinical hypothyroid and euthyroid subjects. Our study demonstrated that chemotactic and mean phagocytic activity was significantly less in those with subclinical hypothyroidism as compared to euthyroid control group (p value= 0.005 and 0.045 respectively). Respiratory burst activities of both unstimulated & stimulated neutrophils were relatively reduced in subclinical hypothyroidism (p value of 0.08 and 0.07). Candidicidal activity was similar in both groups. We conclude that subclinical hypothyroid individuals having excess of thyroid stimulating hormones are associated altered functional characteristics of neutrophils.
Candidicidal activity, Chemotaxis, Neutrophils, Phagocytosis, Respiratory burst activity, Subclinical hypothyroidism
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