Lymphoid system

The immune system has the ability to distinguish self from non self cells ,also has the ability to inactivate or neutralize the foreign molecules such as bacteria ,viruses ,viral infected cells or tumor cells ……etc . The cells of immune system are 1-distributed all over the body 2- arrange themselves into small spherical nodules called (lymphatic nodules ) or 3- organized into organs .

Antigens: A molecules that are identified by the cells of immune system is called Antigens that may elicit a response of these cells . Antibodies : Antibodies belong to the immunoglobulin (Ig) protein family , free molecules of plasma cells are secreted by plasma cells that arise by proliferation and terminal differentiation of B lymphocytes whose receptors identify and bind specific Antigen .

Classes of antibodies

Cytokines : They are peptides or glycoproteins that are produced by cells of immune system such as macrophage , lymphocytes and leukocytes , they influence both the humeral and cellular responses .

Lymphocytes They are B ,T and natural killer cells Distinguished only by ICC Origin ,differentiation Primary or central L organs and secondary or peripheral L organs

B lymphocytes After the exposure of B lymphocyte to Ag ,they recognize it and several cycles of cell proliferation begin then followed by redifferentiation of these cells into plasma cells .This population of plasma cells secrete Antibodies against that Ag .Activation of B cells require the assistance of subclass of T cells called T helper lymphocytes .Not all activated B cells become plasma cells some remain memory cells which react rapidly to a second exposure to the same Ag .

T lymphocytes Helper lymphocytes or CD4 are responsible for their interaction with B cells to promote their differentiation into plasma cells ,activation of macrophages for phagocytosis ,activation of cytotoxic lymphocytes and induction of an inflammatory reaction . Cytotoxic lymphocytes or CD8 can act on foreign cells and virus infected cells by means of two mechanisms .In one they attach to the cells to be killed and release protein called porforins that create holes in the cell membrane of target cells ,with consequence cell lysis .In other hand ,they attach to a cell and kill it by triggering mechanisms that induce programmed cell death or apoptosis .

Natural killer lymphocytes (NKL) : NKL lack the marker molecules characteristic of B or T lymphocytes .They comprise 10-15% of the lymphocytes in the circulation .Their name derive from the fact that they attack virus infected cells ,transplanted cells and cancer cells without previous stimulation .

Antigen presenting cells APC: APC are heterogenous cell population that include: 1- (MPS) Macrophage and dendritic cells present within the epidermis are called Langerhans cells, and Kupffer cells (liver) and dendritic cells of spleen and lymph node these cells have many processes and upon capturing the Ags, they retract their processes move towards the dermis and may enter a lymphatic vessel. 2- B lymphocyte and epithelioreticular cells

MHC & Ag presentation MHC is a complex of chromosome loci that encode several proteins known as class I and class II MHC molecules. These molecules are unique for each individual. All nucleated cell have class I, while Antigen presenting cells contain class II. MHC synthesized by polyribosomes and inserted in the membrane of RER. On their way to the cell surface, they couple with small peptides 10-30 amino acid

Follicular Dendritic cells

Types of immune response : The two basic types of immune response are the innate and adaptive response . The innate response occur through the action of neutrophils , macrophages , mast cells and natural killer cells , is fast ,non specific and does not produce memory cells . The adaptive response which depend on the initial recognition of Ag by B or T cells is slower , more specific and produce memory cells . The adaptive response are classified into humoral and cellular responses . Humoral response is accomplished by antibody produced by plasma cells derived from B cells . Cellular reesponse is mediated by T cells that 1-secret cytokins that act on B , T cells and on inflammatory cells such as neutrophils and macrophages and 2-attack foreign cells such as virus infected cells , parasites and tumor cells .

Immune diseases 1- Allergic diseases 2- Immunodeficiency diseases 3- Autoimmune diseases

Mucosa Associated Lymphoid Tissue 1- Diffuse Lymphatic tissue The mucosa and submucosa of the digestive tract ,respiratory tract ,genitourinary tract contain a large amount of diffuse collection of lymphocytes ,IgA secreting plasma cells ,APCs. and lymphatic nodules

2- lymphatic nodules localized collection of lymphocytes found also in the wall of GIT, Respiratory passages, Genito-urinary tract, etc…, these called lymphatic nodules They are2 types: primary and secondary Secondary nodules has 2 important structures: Germinal centre and mantle zone

Tonsils The tonsils is a lymphoid tissue that lies beneath and in contact with the epithelium of the initial portion of the digestive tract .Depending on their location ,tonsils in the mouth are called palatine ,pharyngeal and lingual .

Follicular tonsilitis

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