lymphocytes

Lymphocytes are a class of agranular leukocytes (white blood cells, WBC) that include B lymphocytes ( B cells) and T lymphocytes (T cells).

B cells are lymphocytes coated with immunoglobulin BCRs that participate in humoral immunity by producing antibodies in response to antigen stimulation. T cells or T lymphocytes are specialized lymphocytes distinguished by their TCR surface receptors.

B lymphocytes are named for the bursa of Fabricus. Types of B cell:
● B-1
● B-2
● Plasma B cells
● Memory B cells

'T' lymphocytes initially develop in the thymus, and differentiate peripherally into several functional subsets of cells:
● Cytotoxic T cells – CTL, Tc – CD8 +
● Helper T cells, effector T cells – Th – CD4 +
● Regulatory T cells –Treg (formerly termed 'suppressor' T cells)
● Natural killer T cells – NKT (different than NK cells)
● γδ T cells

NK cells are distinct from natural killer T cells. NK, natural killer cells constitute a corps of circulating lymphocytes that are constitutively specialized to attack cancerous cells and virus infected cells. Preprogramming for target recognition coupled with the absense of need for backup by a clone of identical cells, renders NK cells capable of rapid (innate) response to pathogens. NK attack involves the exocytosis of cytoplasmic granules containing perforin and granzymes. Perforin forms pores in the plasma membrane of attacked cells through which serine-protease granzymes enter, cleaving caspase precursors and triggering apoptosis.

Tables  Fc receptors  Immune Cytokines  Immunoglobulins