Regulatory T (Treg) cells hold centre stage in regulating the immune responses in most viral infections. However, their involvement in chikungunya infection is unexplored. In the current study, the frequencies and functionality of peripheral Treg and T effector (Teff) cells were assessed during different phases of chikungunya by flow cytometry and in-vitro cytokine assays. Treg cells were also studied in rheumatoid arthritis (RA) patients, whose symptoms closely mimic chronic chikungunya arthritis patients. Frequency of Treg cells was lower in acute and chronic chikungunya arthritis patients than in recovered individuals and controls, and comparable among recovered individuals and controls. Treg/Teff ratio was lower in acute than in chronic chikungunya arthritis patients, recovered individuals and controls. Higher secretion of CHIKV specific IL-10 was observed in recovered individuals than in acute, chronic chikungunya arthritis patients and controls. Frequencies of Treg and Teff cells were higher and Treg/Teff ratio was lower in RA patients than in chronic chikungunya arthritis patients. The results indicate that reduction of Treg cells was associated with ongoing CHIKV infection and normalization of Treg cells with resolution of disease. Contrasting phenotypic data in RA and chronic chikungunya arthritis suggest an altogether different mechanism of Treg-mediated pathology in both arthritis conditions. Overall, our preliminary study, suggesting an association of peripheral Treg cells and IL-10 with recovery from chikungunya, may provide insight into chikungunya disease prognosis and warrants further study.

This article was designed to determine variations in phenotypic composition of fresh and frozen PBMCs for assessing utility of cryopreserved PBMCs for phenotypic assays. Relative percentages of effector memory cells increased significantly as against percentages of naïve cells which showed significant decrease after cryopreservation in HIV-uninfected samples. These differences were not significant in HIV-infected individuals. There was no significant difference in the expression of activation markers in fresh and frozen PBMCs except the HLA DR expression on CD8 cells in HIV-infected individuals, which was significantly decreased in frozen PBMCs. Thus, cryopreservation resulted in differential effect on phenotypic composition of PBMCs in HIV-infected and -uninfected individuals.