CLS 1113 Introduction to Clinical Laboratory Practices

1. CLS 1113Introduction to Clinical Laboratory Practices T - Cell Function, Antigens

2. Surface Markers on Lymphs • Lymphocytes express many molecules (proteins) called “Markers” on the cell surface which are used to differentiate cell populations, ETC., i.e. B and T cells • Systematic Nomenclature: CD (Cluster of Differentiation) • Groups or Clusters of Monoclonal antibodies that bind to a specific marker.

3. CD Markers • CD4 is the Marker expressed on T helper cells. T helper cells are very active in our cell mediated immunity. • The HIV virus attaches to the CD4 markers on T cells (route of entry); that is why HIV patients progressively lose their immune function. • CD8 cells are T suppressor cells / cytotoxic T cells. CD8 cells help keep our immune system under control and help fight tumors (cytotoxic). • The CD markers on our white cells change as the cell matures helping us define maturity or age of the cells.

4. T Lymphocytes • 60-80% Circulating Lymph’s • Enter thymus • Cortex • Medulla • T Cell Differentiation… • Mature T Cells • T cells recognize antigen ONLY when it is presented on the surface of another cell

5. T - Helper Cells • CD4 receptor • 2/3 peripheral T Cells • Recognize antigen ONLY in association with MHC class II products • Type 1 TH cells: Interacts with macrophages helps them destroy intracellular pathogens • Type 2 TH cells: Help B cells with Ab production Cytotoxic T Cells • CD8 positive • 1/3 peripheral T cells • Recognize antigen ONLY in association with MHC class I products

6. Cell Mediated Immunity T Cell activation • Result of antigen recognition by T cells is the synthesis of effector proteins: LYMPHOKINES • Second messengers: influence the activity of other cells. • Regulate: intensity and duration of immune response • Cytokines

7. Antigens An antigen is a foreign substance capable of eliciting an IMMUNE RESPONSE. Antigen (Immunogen) Characteristics • Size: • Chemical composition: • Complexity: • Foreign:

8. Types of antigens Autoantigens • Antigens that belong to the host. Alloantigens • Antigens from other members of the host’s species (blood types, transplants, grafts, etc.)

9. Types of antigens Heteroantigen • Antigens from another species. Heterophile Antigen • An antigen that exists in nature (plant or animal) so structurally similar to host antigen that there is resultant cross reactivity with the corresponding antibody. • Example:Human Blood Group A antigen and pneumococcal bacteria.

10. Hapten • A hapten is a molecule that can act as an epitope but is incapable by itself of eliciting an antibody response. • To produce a response, the hapten must be bound to a carrier. • Example: Medications are haptens, they are made small enough not to be recognized by the body as foreign. Occasionally, a medication will bind to something like a red cell and become immunogenic.

11. Major Histocompatability Complex (MHC) • The MHC is a group of genes that code for the expression of the antigens on nucleated cells. • These antigens are called “Human Leukocyte Antigens” (HLA) because they were thought to occur only on white cells.

12. HLA antigens • Class I HLA antigens are coded by MHC I genes. • Class I molecules present antigens to CD8 cells (fight tumors, viruses, and parasites) • Class II HLA antigens are coded by MHC II genes and are involved in antigen recognition by CD4 cells. • As a summary, both molecules transport antigens to the surface of antigen presenting cells to be recognized by the corresponding T cell (either CD4 or CD8)