I. INNATE - called natural, native, genetic, constitutional; based on physiological, anatomical, and biochemical differences A. SPECIES - many microbes can infect only certain species B. RACIAL - certain classes or ethnic stocks of a species are resistant or susceptible to given infectious agents C. INDIVIDUAL - individuals having differing levels of resistance or susceptibility; differences are due to factors such as: genetic defects, age, hormonal balance, nutritional status, and unexplained unknown factors II. ACQUIRED IMMUNITY - based on responses by the immune system A. ACTIVE - body is stimulated to produce antibodies as a result of microbial challenge or insult; provides long term protection; antibodies (Ab) and sensitized T cells are produced in the process and continue to circulate in the blood and lymph 1. ARTIFICIALLY ACQUIRED, ACTIVE - follows exposure to prepared antigens such as toxoids, killed or inacti- vated microorganisms or attenuated microorganisms 2. NATURALLY ACQUIRED, ACTIVE - follows infection that has been acquired in day-to-day activities B. PASSIVE - the body receives antibodies or immune product from some outside source; thus the body is NOT stimu- lated to produce its own antibodies; this type of pro- tection is of short duration (until the acquired Ab are broken down or used up) 1. ARTIFICIALLY ACQUIRED, PASSIVE - follows the injec- tion of immune products that were obtained from another species or from members of the same species 2. NATURALLY ACQUIRED, PASSIVE - results from the trans- fer of immune products from one individual to another under natural circumstances (transplacental transfer) Antigens (Ag) ANTIGENS, also called IMMUNOGENS, cause the body to produce a highly specific immune response in the form of ANTIBODIES (Ab) and/or SPECIALLY SENSITIZED CELLS. The vast majority of antigens are proteins, large polysaccharides, or combinations of either (nucleoproteins, lipoproteins, glycoproteins). Because they represent macromolecules that are normally not present in the body they are called "NON-SELF" molecules. Milk proteins, bee venom, hemoglobin molecules, bacterial toxins and various bacterial and viral components may serve as antigens. Only a portion of the antigen is attached to the antibody. The portion of the antigen (Ag) where the Ag and Ab interact is called the ANTIGENIC DETERMINANT SITE. A large antigen may have several antigenic determinant sites. These antigenic determinants are like fingerprints to which the various parts of the immune system respond after they have been identified. The nature of this interaction depends upon the size and shape of the antigenic determinant site in relation to the chemical structure of the antibody. Certain low molecular weight substances, which by themselves are initially NOT antigenic, can become antigenic when they become attached to carrier molecules (such as proteins or polysaccharides). These low molecular weight substances are called HAPTENS. Once an antibody has been formed against a hapten-carrier complex, the hapten alone will stimulate further Ab production. The beta-lactam backbone of the penicillin molecule may become attached to serum proteins in some persons. Antibodies are formed against this new large complex and subsequently penicillin and all other molecules with the beta-lactam backbone become recognizable Ag's. Normally a person's own chemical substances do not stimulate an immune response because they are interpreted as "SELF" molecules. When a person's tolerance of SELF molecules breaks down, an immune response may occur. This may result in damage or destruction of various cells or tissues and may be called an AUTO-IMMUNE RESPONSE. Antibodies (Ab) ANTIBODIES are proteins that are produced by B-lymphocytes in response to the presence of an antigen. The Ab is capable of combining specifically with that Ag. The Ab has more than one combining site. Antibodies belong to a group of proteins called GLOBULINS. Because they are involved in the immune response they have a general name of IMMUNOGLOBULINS (Ig). Immunoglobulins are found in the blood serum, mainly in the GAMMA fraction, and in other bodily secretions. Antibodies are often identified in many different ways. We have seen that because of their protein organizational level they are globulins. Being involved in immune responses these protein antibodies are called immunoglobulins. Antibodies are sometimes identified functionally. For example Ab's that neutralize toxins are called ANTITOXINS; those that cause precipitation reactions are called PRECIPITINS. The structure, size, and location of Ab's is sometimes used to identify them. At the present time, five classes of antibody (immunoglobulin) are recognized based on differences in part of their structure. These classes of Ig,s are designated IgM, IgG, IgA, IgE, and IgD.Back to HomepageClasses of Immunoglobulins Ig-M the very first time that we are exposed or challenged by an new antigen (one the body has never recognized before) this very large antibody molecule is formed; its large size prevents it from leaving the general circulation; the anti- gen becomes identified by being phagocytized by macrophages which are then contacted by B-cells; these B-cells begin to produce the IgM and come in contact with T-cells which then become sensitized and stimulate the B-cells to change into antibody factories known as plasma cells; this sequence begins a production of a second class of Ig's known as IgG's IgM antibodies are involved in ABO blood typing reactions, Complement Fixation reactions and enhanced phagocytosis Ig-G for long-term immunity to develop IgG antibodies must be produced; 80-85% of all circulating Ab's are IgG; they are found in the blood, the lymph, and the intestinal fluids as they are capable of crossing the walls of blood vessels and entering the tissue fluids; they protect against circu- lating bacteria and viruses; they can neutralize bacterial toxins and aid phagocytic cells; they also participate in Complement Fixation reactions and are the type of Ab found in the first mother's milk and passed on to new babies; this group can be subdivided into at least four subclasses Ig-A about 15% of all Ab's are of this type; they are found in the serum and in secretions of the gastrointestinal tract the respiratory system, and other mucous membranes; their main function is to prevent pathogens from attaching to the surfaces of mucous membranes; secretory IgA in colostrum provides passive immune protection to the gut of the newborn against microbes that might cause gastroenteritis; in resp- iratory mucous IgA may neutralize allergens Ig-E making up less than 1% of the total serum Ig's this group is responsible for some of the most severe immunologic reactions called hypersensitivity or allergic reactions; this Ig binds to tissue basophils (called mast cells) and in combination with the antigen causes the basophil to degranu- late (break open its lysosomal granules) and release histamine, heparin, leukotrienes and serotonin which are responsible for most of the reactions associated with allergic or hypersensitivity reactions Ig-D little is known about this type of Ig which makes up about 1% of all AB's; it may be involved in reactions against cow's milk; in fetal lymphocytes it may determine which cells should be destroyed so that they do not cause autoimmune reactions