Module 1: Introduction

Lecture 6: Adaptive immune system (Part II)

6.1 Cells of the adaptive immune system

Major cells of the adaptive immune system includes following.

Lymphocytes

Antigen presenting cells

Effector cells

Lymphocytes are the main cells which can recognize the antigen and produce an antibody in order to eliminate the antigens. They are considered as a mediator of both humoral and cellular immunity. B lymphocytes are the only cells in the body capable of producing antibodies. B lymphocytes recognize the extracellular antigens and are differentiated into the plasma cells. T lymphocytes recognize the intracellular antigens and they either help in their phagocytosis or direct killing of the infected cells. T lymphocytes are activated by the antigen loaded over the major histocompatibility complex (MHC) molecules, which are expressed on the surfaces of other cells. T lymphocytes are divided into different subsets which are specific for certain specialized functions. Helper T cells are the subsets of T lymphocyte that secretes the cytokines and help in the proliferation and activation of T lymphocyte. Helper T cells also activate the B cells (to secret the antibody), macrophages and other leucocytes by the virtue of the cytokines. Cytotoxic T lymphocytes kill the cells infected by viruses or other intracellular pathogens. Regulatory T cells help to reduce or inhibit the immune response and are negative regulators of immune system. Natural killer cells are involved in the innate immunity against viruses or other intracellular pathogens. Different classes of lymphocytes can be identified and differentiated by the expression of their surface receptors called cluster of differentiation (CD).

Antigen-presenting cells are mostly the dendritic cells which capture the antigens, transport it to the lymphoid organs and present the antigens to naïve lymphocytes in order to activate the immune response.

Effector cells of the immune system mainly include activated T lymphocytes, mononuclear phagocytes, and other leukocytes. Effector cells are required to complete the immune cascade, i.e. to eliminate the microbes.