An immune disorder is characterized by the failure of the immune system to function properly. Clinical manifestations of immune disorders include allergies/ hypersensitivities, autoimmune diseases, immune deficiencies, and immunoproliferative disorders.

I. Hypersensitivity (allergy) is an abnormal immune reaction in individuals who have been previously exposed (sensitized) to a certain kind of a non-pathogenic allergen (pollen, bee’s venom etc.).
Types of hypersensitivity.
1. Anaphylatic reactions (Type I).
Type I reactions take place when an antigen combines with IgE antibodies and IgEs consequently bind to either mast cells (skin and respiratory tract) or basophils and cause these cells to release histamines and other chemical defense mediators. The released chemicals trigger the allergic reaction, usually through inflammation.
Systemic anaphylaxis (anaphylactic shock) is an adverse immunologic reaction that takes place during re-exposure to the same antigen (usually via injection such as insect bites) and results in the loss of blood pressure due to blood vessel dilation.
Localized anaphylaxis is associated with ingested or inhaled antigens and results in sneezing, coughing, and hives.
To reduce allergic symptoms, a person can undergo de-sensitization (subcutaneous injections of increasing doses of an antigen).
2. Cytotoxic reactions (Type II).
Cytotoxic reactions involve the activation of complement by the IgG (IgM)/ antigen complex. During blood transfusions, type II reactions are involved in the destruction of the donor’s red blood cells.
3. Immune complex reactions (Type III).
Type III reactions (serum sickness) are generated in response to soluble antigens from injection of a foreign protein or serum. When antibodies react with the antigen in serum, soluble circulating immune complexes form, which can diffuse into vascular walls, where they may initiate fixation and activation of complement, subsequently causing inflammatory damage (glomerulonephritis is a type III reaction).
4. Cell-mediated reactions (Type IV).
Type IV reactions involve T cells (TD and TC) and have a delayed onset. Cell-mediated reactions are involved in the skin test for tuberculosis, as well as in reactions to poison ivy and allergic reactions to metals and latex (allergic contact dermatitis).

II. Autoimmune diseases.
Autoimmune diseases are immune reactions caused by malfunction in the self/ non-self recognition system. The immune system normally acquires self-tolerance by clonal deletion of autoreactive T cells during the early stages of development and by functional suppression of autoreactive B and T cells later in life. When a failure in the maintenance of self-tolerance takes place, an autoimmune response is generated. The autoimmune response is characterized by clonal expansion of autoreactive lymphocytes and the production of antibodies against antigens of normal body tissues.
1. Type I autoimmunity involves antibodies that attack self cells.
2. Type II autoimunity (cytotoxic autoimmune reactions) cause such diseases as Graves’ disease and myasthenia gravis.
3. Type III autoimmunity (immune complex autoimmune reactions) is involved in systemic lupus erythematosis and rheumatoid arthritis (RA). RA is triggered by an unknown antigen, perhaps a bacterial or viral infection. During RA, immune complexes consisting of IgM, IgG, and complement are deposited in the joints, where they attack cartilage and bone of the joints.
4. Type IV autoimmunity (cell-mediated autoimmune reactions) are involved in Hashimoto’s thyroiditis and insulin-dependent diabetes mellitus.

III. Reactions related to the Human Leukocyte Antigen (HLA) complex.
The HLA complex consists of histocompatibility antigens that are individual-specific. Some HLAs are associated with increased risk of certain disorders. HLAs are used for compatibility analysis in transplant surgery.

IV. Immune deficiencies.
Immune deficiency is the lack of a sufficient immune response. Immune deficiencies can be either congenital (persist from birth) or acquired. Some cancers result in acquired immune deficiency. Tumor cells avoid detection because of the lack of antigens on their surface and can suppress the immune system by reducing the effectiveness of TC cells.
Microbial methods of cancer therapy:
- administering attenuated bacteria endotoxins that stimulate the production of tumor necrosis factors (TNF) by macrophages.

VI. Acquired Immunodeficiency Syndrome (AIDS).
- AIDS is a late stage of a disease caused by human immunodeficiency virus (HIV).
- HIV was probably acquired by humans through horizontal transmission from monkeys in the first quarter of the 20th century.
- HIV is a retrovirus. It carries two identical strands of RNA, the enzyme reverse transcriptase, and a phospholipid envelope with glycoprotein spikes on the surface.
- HIV’s spikes recognize CD4 receptors on the surface of TH lymphocytes and macrophages.
- Once the HIV RNA is reverse transcribed into DNA, it can integrate into the host cell genome and remain there as a provirus. Alternatively, HIV can reproduce inside the host cell at low levels without leaving the cell (latent infection).
- The typical progression from the initial HIV infections to AIDS is 10 years.
- The HIV transmission requires exchange of bodily fluids.
Stages of HIV infection:
1. Category A, asymptomatic. The virus is not actively reproducing and exists in either the provirus or latent form.
2. Category B, symptomatic. Early signs of immune failure are evident, yeast infections persist.
3. Category C, developing of AIDS. The signs include the persistence of secondary infections.
Targets for HIV treatment:
- reverse transcriptase inhibition (competitive, by preventing viral DNA synthesis, or non-competitive, by interfering with the enzyme structure);
- protease inhibition (results in prevention of the viral particles assembly);
- integrase inhibition (prevents viral DNA integration into the host cell genome);
- prevention of viral adhesion to host cells (under experimental stages).
Microbial methods of HIV treatment:
- Some vaginal microbiota (L. crispatus and L. jensenii) produce bacteriocins against the HIV virus.
Genetically engineered viruses (VSV) can specifically recognize and destroy infected T cells displaying the HIV epitope.