Deficient Immunity

There are a number of conditions that cause deficient immune responses.

Inherited Immunodeficiency

Inherited immunodeficiency disorders can result in inability to produce antibodies, such as:

Acquired Immunodeficiency

Deficient immune response can also be the result of any number of acquired conditions, including:

Excessive Immune Response

There are several circumstances in which responses of the immune system are inappropriate, unwanted, or excessive. These include:

Allergy

Allergies are undesirable inflammatory responses to environment exposures that are harmless to most people. A wide variety of substances can trigger an allergic reaction (referred to as allergens), including plant pollen, foods (e.g., peanuts, soy, seafood, eggs), animal dander (e.g., from cats, dogs or other furry animals), insect stings (e.g., bee sting allergy), mold, medicines. Some individuals are "atopic," meaning that they have an inherited predisposition to developing allergies. Exposure to an allergen in an allergic individual triggers the secretion of IgE antibodies, which trigger the release of histamine and other mediators from mast cells and basophils when the antibody binds to the allergen. The magnitude of the resulting inflammatory response can vary widely, ranging from mild to moderately severe local symptoms (e.g., allergic rhinitis/conjunctivitis, eczema or hives) to life-threatening conditions such as asthma and anaphylactic shock.

Autoimmune Disorders

Autoimmune disorders are those in which an individual's immune system attacks its own tissues and organs. The underlying causes of autoimmune disease are not well understood, but one theory is that infections or other injuries to tissues cause alterations that confuse the ability of our immune system to distinguish between "self" and "non-self".

Common autoimmune disorders include:

and there are many other forms of autoimmune disease

Transplant Rejection

As noted earlier, the MHC molecules are an means of distinguishing between "self" and "non-self". The MHC molecules in humans are referred to as the human leukocyte antigens (HLA antigens). The probability of transplant rejection is reduced when there is a close match between HLAs of donor and recipient. Rejection of transplanted tissue is mediated primarily by the adaptive immune system through cytotoxic T cells and B cells which differentiate into antibody-producing plasma cells.BB

Blood Transfusion Reactions

Our red blood cells have glycoproteins that can be antigens. The four major "types" of glycoproteins on human red blood cells are classified as A and B, but the antigens on our red blood cells are co-dominant, meaning that one's blood type is determined by two alleles, neither of which is dominant. Therefore, the major blood types in humans are A (AA or AO), B (BB or BO), AB, and O. Another important antigen on red blood cells is the Rhesus or "Rh factor" which is classified as positive (+) or negative (-). Blood banks will match donor and recipient blood types to minimize incompatibilities, because transfusion of incompatible blood can result in destruction of the transfused blood cells and a sever transfusion reaction.

Cytokine Storm

As described earlier in this module, cytokines are a large family of signaling molecules that play a vital role in orchestrating an inflammatory response and in ramping up the immune response to a pathogen. As a result, there are significant changes in blood vessels that allow proteins, fluid and cellular elements of the blood to leve the circulation and move into tissues to destroy foreign agents or substances. Cytokines are also responsible for activating cells of the immune system and stimulating lymphocytes to divide repeatedly and, in the case of B cells, to differentiate into antibody-secreting plasma cells. Most challenges by pathogens are resolved successfully, and the surge of immune response gradually subsides when the foreign agents have been contained and eliminated. Cytokine secretion subsides, and the large numbers of lymphocytes created through clonal selection also decline as a result of apoptosis. Only a relatively small number of memory cells are left. However, under some circumstances that are not well understood, the immune response does not subside normally. Instead, there is unbridled inflammation within tissues and key organs. Certain types of infection seem to carry a higher risk of cytokine storm, e.g., systemic infection and septic shock, SARS, bird flu, Hanta virus infection, and Ebola.

During the 1918 flu pandemic there was an unusually high death rate among healthy young people between the ages of 20-40. These appeared to be due to respiratory failure as a result of excess accumulation of edema fluid in the lungs as a result of an excessive inflammatory response. A similar phenomenon was noted during the H1N1 influenza pandemic in 2009.


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