Fig. 1.

A

Upon activation naive cells become activated effector T cell (T helperTh1/T cytotoxic Tc1). Activated effector T cells up-regulates TIM-3 (an immuno-inhibitory receptor) which upon binding to its ligand galectin 9 (expressed on innate cells and other immune cells) or available as soluble form, result in apoptosis of TIM-3 bearing effector T cells. This results in dampening of the immune response which might otherwise result in immuno-pathology due to excessive cytokine production by the immune effector cells. Remaining cells down regulates TIM-3 after peak of an immune response. Thus TIM-3-Galectin 9 is an immunoregulatory pathway.

Fig. 1B

High PD-L1 expression is expressed in the thymus and on dendritic cells, where the PD-L1/PD-1 interaction prevents the proliferation and differentiation of naïve T cells. PD-1-PD-L1 pathway is also involved in immune exhaustion. Persistent up-regulation of PD-1 is expressed on tumour-infiltrating lymphocytes, where PD-L1 expression is exploited by malignant cells to avoid immune destruction (an immune evasion strategy by tumor cells).