Figure 7: Proposed mechanism of regulation: Trade-off mechanism and regulation between endogenous melatonin Teffs cells, catecholamines of Tregs cells of lymphocyte sub-population. It may be hypothesized that high level of melatonin in association with its receptor Mel1a and Mel1b along with the cytokines receptor represents a model for bidirectional regulatory loop of arm of Tregs and Teffs cells.