Medical brain notes 12

  FUNCTIONAL COMPONENTS OF THE  IMMUNE SYSTEM Each of the cells in the immune response has a particular role to play. While many of these cells will be discussed in detail in subsequent, a brief review of the functional capabilities is presented here. Macrophages These cells may be divided into two main groups: the dendritic cell and the mature macrophage. The dendritic cell’s major function is to present antigen to the lym-phocyte, and it is the earliest cell to recog-nize foreign antigen.   There are two forms of dendritic cells:  immature  and  mature . The induction of an   adaptive immune response begins when a pathogen is ingested by an immature den-dritic cell. These cells reside in most tissues and are relatively long-lived. As seen in Figure 1.1, they are derived from the same cell myeloid precursor as the macrophage. This immature cell carries receptors on its surface that recognize common features of many pathogens such as cell wall carbo-hy...

TISSUE DAMAGE PATHWAYS Although the major function of the com-ponents of the immune system is to neu-tralize or destroy the invading organisms or antigen, these reactions often cause “bystander” tissue damage as well. These are called  hypersensitivity reactions , and Gell and Coombs conveniently divided them into five types. Hypersensitivity Reactions TYPE I: IMMEDIATE These reactions are those that involve antigens that react with IgE bound to tissue mast cells or basophils. Activation of the mast cell results in the release of large amounts of pharmacologically active sub-stances. These reactions are rapid (hence immediate) and if injected into the skin a “wheel and flare” reaction can be seen within five to ten minutes. Most anti-gens stimulating IgE are either inhaled or ingested. A perfect example of the inhaled antigen is ragweed pollen. The IgE pro-duction requires helper T cells and T-cell-derived cytokines. IL-4 and IL-13 stimulate IgE production while IFN- γ  is inh...

  ANTIBODY PRODUCTION Antibodies for various tests can be pro-duced in a number of different ways, and we will discuss the prototype of each in turn. a.     Polyclonal antibodies : Many mammals   have been used to produce antibodies, ranging from the horse, sheep, and goat down to mice and guinea pigs. Often an animal species is selected for antibody production because it will produce less-cross-reactive antibodies to a given tis-sue. Larger mammals, such as goats and sheep, are used to obtain larger volumes of serum to be used therapeutically in humans. A recent fear has been that ani-mals such as sheep or cows may have eaten animal foddage contaminated with prion disease. Thus, polyclonal antibody production for therapeutic uses has often been limited to countries like Australia or New Zealand where there have been no recorded cases of prion disease in mammals.   b.     Monoclonal antibodies : Over the past   two decades, the revolutio...

  Measurements of Immunoglobulins The introduction of automated machines to measure immunoglobulins and other proteins has proceeded rapidly in recent decades. Most clinical immunology laboratories rely almost exclusively on these machines, and research labs are also intro-ducing these automated techniques at a rapid pace. Precise measurement of serum immunoglobulins is an essential corner-stone in this area and is important for repeated and serious infections secondary to immunosuppressive agents, immunode-ficiencies, in lymphoproliferate disorders, and for detection of autoantibodies. The main principle behind this test is related to the formation of immune com-plexes between the antibody and a given antigen. If the concentration of antigen– antibody complex is low, then the immune complexes remain in suspension as fine particles, which can disperse a beam of light. As the complexes increase with concentration of antibody, the complexes will precipitate, and light scattering will...

  Fluorescein-Activated Cell Sorter With the renewed interest in the role of lymphocytes in disease states over the past thirty years, a systematic study of the mark-ers present on B and T lymphocytes has been undertaken. The knowledge that many such markers exist on a given cell was made possible by the introduction of monoclonal antibodies specific for each marker. Thus, antibodies could quickly identify lympho-cytes as B (CD19) or T lymphocytes (CD3) and later into helper (CD4) or suppressor cells (CD8) and many other markers.   Figure 2.3  Schematic depiction of cell separation on a flow cytometry   machine or fl uorescein-activated cell scan. The different cell populations are separated both by size (forward scatter) and granularity (side scatter) and  a given population is then separated into B or T cells and within the T cells into helper (CD4 + ) and suppressor (CD8 + ) cells. Isolation and purifi cation of a given subset of cells can be achieved by a fl...