IMMUNOLOGY

Detailed explanation-1: -When a lymphocyte encounters its antigen in a peripheral lymphoid organ, the binding of the antigen to the receptors activates the lymphocyte, causing it both to proliferate and to differentiate into an effector cell.

Detailed explanation-2: -Antigens trapped in the lymph nodes are responsible for the activation of lymphocytes present in lymph nodes. Thus, they trigger the immune response as well.

Detailed explanation-3: -They are activated on the surface of antigen-presenting cells, which mature during the innate immune responses triggered by an infection. The innate responses also dictate what kind of effector cell a helper T cell will develop into and thereby determine the nature of the adaptive immune response elicited.

Detailed explanation-4: -CD4+ T cells are activated in regional lymph nodes and migrate to skin to initiate lymphedema.