IMMUNOLOGY

Detailed explanation-1: -In the spleen, T cells are passively released in the blood flow from the arterioles in the red pulp and marginal zone area. In contrast, T cells in the blood are actively captured on high endothelial venules in lymph nodes by the coordinated actions of CCR7 and several adhesion molecules.

Detailed explanation-2: -T Helper (Th) Lymphocytes T helper cells recognize viral peptides in association with class II MHC protein, usually on the surface of an antigen-presenting cell (APC). These interactions result in T helper cell activation, proliferation and differentiation, providing the affinity of binding is sufficiently high.