The tissues of the immune system consist of primary and secondary lymphoid organs. Primary organs include the thymus and bone marrow, where T and B cells mature. Secondary organs include the spleen, lymph nodes, and mucosal tissues, where immune cells are activated. Mature T cells proliferate and migrate to sites of infection, while mature B cells give rise to plasma cells and memory B cells upon activation. The immune system tissues work together to recognize pathogens and mount targeted responses through cellular and humoral immunity.

1. TISSUES OF THE IMMUNE SYSTEM
The tissues of the immune system consist of the generative lymphoid organs, in which T and B lymphocytes
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mature.
Mature T cells; activated T cells proliferate + migrate to sites of inflammation to eliminate infection.
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Mature B cells; activated b cells gives rise to plasma cells and memory cells.
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Organs of the immune system
A) primary lymphoid organs
thymus (develop mature T cells)
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bone marrow (develop mature B cells)
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fetal liver (hematopoiesis - making blood cells)
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B) secondary lymphoid organs (site of immune activation):
spleen
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lymph nodes
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mucosal-associated lymphoid tussle (MALT)
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1) Lymph Nodes;
This gland works in conjunction with the spleen; acts as a filter for the lymph, a place where white blood cells
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fight infection.
Bean-shaped filters that cluster along the lymphatic vessels of the body.
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They function as a cleanser of lymph as wells as a site of T and B cell activation.
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2) Thymus;
Produces white blood cells that destroy germs. (T-cells)
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An immune organ located near the heart. This is the site of T cell maturation and is larger in children and
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adolescents.
3) Spleen:
Works in conjunction with the lymph nodes; recycles red blood cells; a place where white blood cells fight
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infection.
An organ that is part of the lymphatic system; it produces lymphocytes, filters the blood, stores blood cells, and
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destroys old blood cells.
4) Appendix:
A safe house for beneficial bacteria, protects rather than harms, good bacteria needed for digestion.
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A small, fingerlike extension of the vertebrate cecum; contains a mass of white blood cells that contribute to
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immunity.
5) Bone Marrow;
Develops stem cells that mature into white blood cells (B-Cells) that fights infection and destroys germs.
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A soft tissue inside the bone that produces blood and immune cells.
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6) Tonsils;
help protect from infection by trapping germs coming in through your mouth and nose and destroy germs in
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your throat.
A ring of lymphoid tissue around the entrance to the pharynx.
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7) Adenoids;
help protect from infection by trapping germs coming in through your mouth and nose and destroy germs in
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your throat.

2. Lymphoid tissue located behind the nasal cavity.
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8) Lymphatic Vessels;
A system of vessels that carries lymph through the body into the nodes; different from blood vessels; lymph
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drains tissues and contains white blood cells that fight against germs.
Located deeper within the tissues that has lymph flowing to them from the lymphatic capillaries.
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9) Peyer's Patches;
Macrophages captures and destroys bacteria, prevents them from penetrating through intestinal walls.
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10) Skin;
The first line of defense; if not unbroken cannot be pierced by most microbes.
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4 Types of Immune Cells
1) Leukocytes; White Blood Cells.
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2) Plasma Cells; Make and secrete antibodies.
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3) Macrophages; Engulf invading particles
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4) Mast Cells; Trigger inflammatory response
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Principal cells of the immune system (4 types of Lymphocytes;)
1) B Cells; Recognize foreign antigens: secrete antibodies to guide attack.
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2) Cytotoxic T Cells; Recognize and attack cancerous and infected cells.
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3) Helper T Cells; Help Activate B Cells and Cytotoxic T Cells: Are attack by HIV. Type of Lymphocyte.
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4) NK Cells; Kill Cells with guidance from antibodies.
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Naive and effector lymphocytes and Memory cells
1) Naive cells; are mature T or B cells that have not been activated by an microbe antigen yet.
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They pass through the circulation in lymph nodes or wait in the tissue for a breach.
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Naive T lymphocytes flow through the peripheral organs and recirculate until activated by an antigen.
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2) Effector cells; are activated in the lymph node but go to the site of infection where the antigen may be
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located.
have been activated in some way by the presence of a pathogen. These cells elicit an antimicrobial defense to
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protect or eliminate pathogens. Most effector cells die after some time, but some live on.
3) Memory B cells; live on after the immune response dies down. They can change isotopes of antibody
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immunoglobulin to improve affinity and specialize for particular antigens. Improve reaction to second exposure.
T cells
recognize, ingest and destroy microbes, display their peptides to B cells activating their humoral response
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Types of T cells
1) Cytotoxic T Cells( CD8 cells); Destroys host cells that harbour anything foreign. They are directly
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responsible for cell mediated immunity.
2) Regulatory cells; inhibit multiplication of cytokine secretion by other t cells *limit immune response.
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3) Supressor T Cells; Turn off an immune response.
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4) Memory T Cells; Jump start an immune response to an antigen that was previously present in the body.
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They remain in the body.
5) Helper T Cells(CD4 cells); Modulate activities of OTHER immune cells.
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helps promote t cell and b cell action and non specific resistance.
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3. The major role of Th1 cells is to secrete IFNɣ and A major activity of IFNɣ is to activate.
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Th1;
response is characterized by the production of interferon - gamma.
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secrete IL-2, IL-12, IFN gamma, TNF-beta;
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produce IFNγ and promote cellular immunity
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activate macrophages, amplifying their cytokine secretion capacity and potential for
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presentation of antigens;
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activate synthesis of IgG but not IgE;
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are involved in delayed hypersensitivity reactions;
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are activated by signals from intracellular bacteria and viruses;
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Th2
secrete IL-4, IL-5, IL-6, IL-10;
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activate the synthesis of IgE;
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stimulate proliferation and activation of eosinophils;
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are stimulated by allergens or parasite components.
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Th2 response is characterized by the release of interleukin 4
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Th2 produce IL-4 and promote humoral immunity
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B cells
B cells - secrete antibodies that bind to antigens, or initiate the complement system,
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Differentiate into plasma cells and produce antibodies.
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are formed in the bone marrow.
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are located in the germinal centers of lymph nodes, white pulp of the spleen, and GALT.
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B-cell activation occurs in the secondary lymphoid organs such as the spleen and lymph nodes.
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Six Types of B-Cells; Plasmablast, Plasma Cell, Memory B-Cell, Follicular B-Cell, Marginal Zone B-Cell and
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Regulatory B (Breg) Cell.
are five types of antibody IgA, IgD, IgE, IgG, and IgM,
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IgM; is the basic antibody produced by B-cells.
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B lymphocytes;
B lymphocytes are the only cells capable of producing antibodies
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B-lymphocytes function in the humoral immunity component of the adaptive immune system by secreting
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antibodies.