Page 165 - Veterinary Histology of Domestic Mammals and Birds, 5th Edition

Immune system and lymphatic organs (organa Iymphopoetica) 147

Haemopoietic stem cell Immature Cell
VetBooks.ir Precursor cell

Immuno-
Non-activated B lymphocyte Non-activated T lymphocyte Non-activated macrophage
competent cell

Antigen
Activated Activated Activated
B lymphocyte T lymphocyte Macrophage presentation,
cell activation

Cloning

Memory cell
formation

Regu- Natural Activated Formation of
Plasma cell Plasma cell Cytotoxic Helper latory killer T
T cell T cell macrophage effector cells
cell cell

Adaptive humoral immune response Adaptive cell-mediated immune response Innate cellular immune response

Target cell/antigen
8.2 Schematic summary of immune cell differentiation and the sequence of events resulting from antigenic
stimulation.

Cells of the adaptive immune response Activated helper T cells have a central role in the elimina-
tion of antigens. They trigger the transformation of mature
T cells
T cells are involved in cell-mediated immunity. They B cells into antigen-specific plasma cells and stimulate the
+
serve to kill other cells through the action of cytokines, activity of various cytotoxic cells. Some CD4 helper T
+
perforin and lytic enzymes including protease (cytotoxic T cells (and some CD8 cells) influence the activity of other
lymphocytes), or to mediate interactions between immu- T cells (suppressor or regulatory T cells), resulting in
nologically active cells. down-regulation or termination of the immune response.
Based on the structure of certain surface molecules, T Helper T cells also differentiate into memory cells that
+
cells are divided into CD4 and CD8 lymphocytes. CD4 + can respond more quickly to renewed antigen exposure.
+
lymphocytes are further subdivided into the groups T 1 Clonal proliferation of T helper cells is prompted by a cas-
H cade of events, including production of interleukin 2.
and T 2 (see Chapter 7, ‘Blood and haemopoiesis’).
H
CD8 LYMPHOCYTES
+
+
CD4 LYMPHOCYTES +
This group of T lymphocytes incorporates the cells CD8 lymphocytes are primarily cytotoxic effector cells.
referred to as helper T cells. The functions and character- Their functions include:
istics of helper T cells include:
· synthesis of cytokines (interferon, tumour necrosis
factor) and
· induction of B cell maturation,
· induction of proliferation of cytotoxic CD8 T cells, · induction of cell death (e.g. via proteases).
+
· synthesis of cytokines, + +
· activation of phagocytic macrophages, As with CD4 lymphocytes, pools of memory CD8 lym-
· stimulation of haemopoiesis and phocytes are formed in response to antigenic stimulation.
· division into subgroups including T 1 and T 2.
H H

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