PATHOLOGY

Detailed explanation-1: -There are two main types of T-cells: Helper T-cells stimulate B-cells to make antibodies and help killer cells develop. Killer T-cells or cytotoxic T-cells directly kill cells that have already been infected by a foreign invader.

Detailed explanation-2: -Helper T cells are arguably the most important cells in adaptive immunity, as they are required for almost all adaptive immune responses. They not only help activate B cells to secrete antibodies and macrophages to destroy ingested microbes, but they also help activate cytotoxic T cells to kill infected target cells.

Detailed explanation-3: -In the thymus, T cells multiply and differentiate into helper, regulatory, or cytotoxic T cells or become memory T cells. They are then seeded to peripheral tissues or circulate in the blood or lymphatic system.

Detailed explanation-4: -B cells can prime naive CD4+ T cells in vivo in the absence of other professional antigen-presenting cells in a CD154-CD40-dependent manner.