GENERAL IMMUNOLOGY PHT 324 Dr. Rasheeda Hamid Abdalla Assistant Professor E-mail rasheedahamed12@hotmail.com

The Organs & cells of the Immune System

OBJECTIVES Lymphoid Organs Cells of the Immune System

Bone Marrow All cells of the immune system are initially derived from the bone marrow. They form through a process called Hematopoiesis. During hematopoiesis, stem cells differentiate into either mature cells of immune system or into precursors of cells that migrate out of the bone marrow to continue their maturation

Thymus The function of the thymus is to produce Mature T cells. Immature thymocytes, known as prothymocytes, leave the bone marrow and migrate into the thymus.

Thymus Through maturation process referred to as thymic education, T cells that are beneficial to the immune system are spared, while those T cells that might evoke autoimmune response are eliminated. The mature T cells are then released into the bloodstream

Spleen The spleen is an immunologic Filter of the blood. It is made up of B cells, T cells, macrophages, dendritic cells, natural killer cells and red blood cells .

Spleen It captures foreign materials (antigens) from the blood that passes through the spleen. It is considered as an immunological conference center. In the spleen, B cells become activated and produce large amounts of antibody. Also, old red blood cells are destroyed in the spleen

Lymph Nodes It function as immunologic filter for the body fluid known as lymph. Lymph nodes are found throughout the body. Inhabited primarily by T cells, B cells, dendritic cells and macrophages

Lymph Nodes

Cells of the Immune System The cells of the immune system arise from a pluripotent stem cell in the bone marrow. Differentiation of these cells will occur along one of two pathways, giving rise to: Lymphoid progenitor cell. Common myeloid progenitor cell.

Lymphocytes Lymphocytes mediate adaptive immune responses. Only small proportion of the body's lymphocytes are found in the blood. The majority are found in lymphoid tissue.

Lymphocytes B lymphocytes, so called because they complete their development in the bone marrow, and T lymphocytes, so called because they pass from their origin in the bone marrow into the Thymus, where they complete their development. Both have surface membrane-receptors designed to bind specific antigens

B-lymphocytes (B-cells) Upon contact with appropriate antigen, B-cell differentiates into antibody-producing plasma cell. Mediate humoral immunity (antibody production) and have B-cell receptors on their surface for antigen recognition. Generally 10-20% of the lymphocyte are B-lymphocytes

T-lymphocytes (T-cells) Arise from stem cells in the bone marrow. Migrate to the thymus where they differentiate into mature T-cells. Surface proteins expressed (TCR, CD4 or CD8). Leave thymus: Circulate in bloodstream. Go to peripheral lymphoid tissues.

T-lymphocytes (T-cells) Mediate cellular immunity (the production of cytotoxic T-lymphocytes and cytokines). Generally 60-80% of the lymphocytes are T-lymphocytes. Based on biochemical markers on their surface, there are two major classes of T-lymphocytes:

T-lymphocytes (T-cells) T4-lymphocytes (CD4+ T-lymphocytes) have CD4 molecules and T-cell receptors (TCRs) on their surface for antigen recognition. B. T8-lymphocytes (CD8+ T-lymphocytes) have CD8 molecules and T-cell receptors (TCRs) on their surface for antigen recognition.

NATURAL KILLER (NK) CELLS Considered part of innate immunity while B and T cells participate in adaptive immunity. Are lymphocytes that lack B-cell receptors and T-cell receptors. They kill cells bound by antibody.

Granulocytes or Polymorphonuclear (PMN) Leukocytes Another group of white blood cells. Composed of three cell types: Neutrophils, Eosinophils and Basophils, based on their staining characteristics with certain dyes. These cells are predominantly important in the removal of bacteria and parasites from the body. They engulf these foreign bodies and degrade them using their powerful enzymes.

Macrophages When monocytes leave the blood and enter the tissue, they become activated and differentiate into macrophages. Macrophages are important in the regulation of immune responses. They are often referred to as scavengers or antigen-presenting cells (APC) because: They pick up and ingest foreign materials. Present these antigens to other cells of the immune system such as T cells and B cells.

Macrophages Macrophages functions in body defense: Killing of microbes, infected cells, and tumor cells by phagocytosis. Processing antigens so they can be recognized by T-lymphocytes during the adaptive immune responses. Secreting proteins called cytokines that play a variety of roles in nonspecific body defense.

Dendritic Cells Originate in the bone marrow and function as antigen presenting cells (APC). More efficient APCs than macrophages. Found in the lymphoid organs such as the thymus, lymph nodes and spleen. They are also found in the bloodstream and other tissues of the body.

Dendritic Cells Called Langerhans cells when found in epidermis. - Poorly phagocytic. - Immature dendritic cells are found under the skin and mucous membranes where they engulf microorganisms and molecules through phagocytosis and pinocytosis.

Dendritic Cells Like macrophages, dendritic cells engulf the microorganisms and other materials and degrade them with their lysosomes. Dendritic cells produce the same cytokines as the macrophages, namely tumor necrosis factor-alpha (TNF-alpha), interleukin-1 (IL-1), interleukin-6 (IL-6), and interleukin-8 (IL-8).

Mast cells Found throughout the connective tissue of the skin and mucous membranes. They release histamine, leukotriens: chemicals that promotes inflammation by causing vasodilation / increasing capillary permeability and increasing mucous production.

THANKS