B lymphocytes or B cells and T lymphocytes or T cells are the major players in adaptive immune response. In adults, these cells are derived from hematopoietic stem cells in the bone marrow. T cells mediate cell mediated immunity whereas B cells are behind antibody mediated or humoral immunity.

Learn more: Difference between B cells and T cells

T cells like B-cells originate in the bone marrow but maturation takes place in the thymus, therefore called as T-cells. Th cells are the most important cells responsible for overall regulation of specific immune response (regulatory cells).

Th cells and Tc cells

Helper T cells

Cytotoxic T cells

CD4 positive cells

A co-receptor, CD4 surface glycoprotein is present along with T cell receptor

CD8 positive cells

A co-receptor, CD8 glycoprotein is present

Why called Thelper cells?

It "help" the activity of other immune cells by releasing cytokines.

Can activate both B cells, T cells and antigen presenting cells like macrophages and dendritic cells

Kills the infected cells; therefore called cytotoxic cells (toxic to cells)  

Also called Killer T cells or effector cells


Recognizes antigen bound to MHC class II present on antigen presenting cells like B cells, macrophages or dendritic cells

Recognizes antigen in association with MHC class I present on all nucleated cells

Mode of action: Activating B cells for antibody production, secreting lymphokines that activate cytotoxic T cells and B cells, attracting neutrophils and enhance the ability of macrophages to engulf microbes.

Destroys virus infected cells and tumor cells directly either by release of perforins which makes pores on  cell membranes causing lysis, or granyzymes, that induces programmed cell death or apoptosis.

Th cells are crucial for defense against both extracellular and intracellular pathogens.

Tc cells provide protection against intracellular pathogens such as viruses , bacteria and parasites that multiply in the host-cell cytoplasm

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