Page 460 - Atlas of Histology with Functional Correlations

Three types of lymphocytes are T cells, B cells, and NK cells

Supporting or accessory cells are antigen-presenting cells (APCs), including
macrophages and dendritic cells
Originate from hemopoietic stem cells in the bone marrow

T Lymphocytes (T Cells)

T cells arise from lymphocytes that were carried to and matured in the
thymus gland
After maturation, T cells are distributed to all lymph tissues and organs
On encountering antigens, T cells destroy them by cytotoxic action or by

activating B cells
Four types of differentiated T cells: helper T cells, cytotoxic T cells, memory
T cells, and suppressor T cells

Helper T cells secrete cytokines or interleukins when they encounter antigens
Cytokines stimulate B cells to differentiate into plasma cells and to secrete
antibodies
Cytotoxic T cells attack and destroy virus-infected, foreign, or malignant
cells via perforating protein perforin

Memory T cells are the long-living progeny of T cells and respond to the
same antigens
Suppressor T cells decrease or inhibit the functions of helper T cells and

cytotoxic T cells
Maturation of T cells is a very complicated process, involving positive and
negative selection
Most T cells recognize self-antigens and die (negative selection)
T cells that recognize foreign antigens reach maturity and enter the

bloodstream (positive selection)

B LYMPHOCYTES (B CELLS)

B cells remain and mature in the bone marrow, then move to nonthymic
lymphoid tissues and organs

Recognize antigens as a result of antigen receptors on cell membranes and
become activated
Response is more intense when antigen-presenting helper T cells present
antigens to B cells

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