1. قسم تقنيات التحليلات المرضية مادة المناعة النظري- المرحلة الثالثة
Lec2
Cells of immune system
قسم تقنيات التحليلات المرضية
مادة المناعة النظري- المرحلة الثالثة
م.م. رشد اياد عبد الحميد

2. The immune system is a network of cells and organs that extend throughout the body and function as a defense against infection, it has been recognized as a separate body system known as lymphoid system because its main cells are lymphocytes.
The precursors of lymphocytes (stem cell) originate from the yolk sac and liver. Later in fetal development, the bone morrow will be responsible for origination & proliferation of stem cells under control of different, hormones, enzymes & interleukins like IL3 ,IL7

3. Organs of Immune System:
Primary (central) lymphoid organ: site where lymphocyte maturation (Naïve or virgin lymphocyte)
Thymus for T cells maturation.
Bone marrow for B cells maturation.
Secondary (peripheral) lymphoid organ:. Site where Lymphocyte interact with Antigens & other cells.
1. Lymph node: Filters the lymph from Ag
2. Spleen: Filters the blood from Ag
3. Mucosa associated lymphoid tissue (MALT).
Naïve or (virgin) lymphocyte : lymphocyte when mature and ready to leave primary lumphoid organ and go to the secondary lymphoid organ.
The cell of immune system:
1-Lymophocyte: subdivided into T lymphocyte, B lymphocyte, natural killer cell(NK cell).
2-Antigen presenting cell

4. Most virgin Naïve lymphocytes have an inherently short life span and are programmed to die within a few days after leaving the marrow or thymus. However, if a cell receive signals that induce the presence of a specific foreign substance or pathogen (Antigen), it may respond to it by a phenomenon known as activation. In the process it may undergo several successive cell divisions over a period of several days. Some of the resulting progeny cells then revert to the resting state to become memory lymphocytes (cells that resemble the virgin lymphocytes from which they are derived but which can survive for many years). The other progeny of an activated ‘virgin’ lymphocyte differentiate into effector cells, which survive for only a few days to carry out specific defensive activities against the foreign invader.

5. Development of T lymphocytes and B-lymphocytes

6. T lymphocytes:
-They constitute 60-80% of total lymphocytes
Types of T cells:
-T helper (Th): CD4+ cells kills the target Ag in association with class II MHC by secreting of IL s that regulate the immune reactions
-T cytotoxic (Tc) CD8+ kills the target Ag in association with class I MHC
-T regulatory (T reg.): CD4+ and CD25+ (Th 3) regulate immune response.
-Th 17 (CD4+ cells)
-Memory T cell (CD4+ or CD8+)
Function of Th cell: Th cell regulate the proliferation and activity of other cells of the immune system: Th cells regulate the immune system by Interleukins.

8. T cytotoxic (Tc) CD8+
-They are CD4 negative (CD4 --) but CD8 positive (CD8+)
-Recognize antigens on the surface of all nucleated cells:
-Kill host cells that are infected with viruse.
-Recognize and kill cancer cells.
-Recognize and destroy transplanted tissue.
Mechanism of killing:
1-Release protein called perforin which forms a pore in target cell, causing lysis of infected cells.
2-Release tumer necrosis factor(TNF) and Granzymes

10. T cell markers (Receptors & Molecules)
Antigen receptor ; (TCR) heterodimer non identical polypeptide chain linked by disulphide bond divided intoTCR1 α,β while TCR2 γ,δ chains
TCR varies in their a.a. as the variable region of Ig. which make it responsible of diversity, specificity, memory, and self/ non self recognition Unlike membrane-bound antibodies on B cells, which can recognize antigen alone, T-cell receptors can recognize only antigen that is bound to cell-membrane proteins called major histocompatibility complex (MHC) molecules.
Fc receptor for IgG & IgM.
Receptor for sheep RBCs (SRBC receptor);Roseate forming.
Measles virus receptor.

11. Molecules of T Lymphocytes: T cells can be distinguished from one another by the presence of (CD: cluster of differentiation) which are a membrane glycoproteins found on the surfaces of T-lymphocyte.
CD2 ; Present in all T cells
CD3 ; 5 polypeptide chains near TCR for signal transduction . Present in all Tcells
CD4 ; only on Th cells react with class II MHC to control Th cell activation (immune restriction)
CD8; on Tc cells react with class I MHC to control Tc cell activation (immune restriction)
CD 28; on Th cells react with B7 molecules.(Co-stimulatory signal)