It is also known as immune complex reactions. It usually occurs due to excess antibody antigen reactions which have not yet been removed by natural immune cells from blood circulation resulting to inflammation and drawing together of leukocytes. The antigen can either be produced by the body its self in case of an autoimmune infection or foreign. It entails soluble antigens which are not attached to surfaces of cells. Diverse immune complexes sizes are produced if these antigens combine together with the antibodies. Macrophages easily eliminate big complexes compared to smaller ones which put in themselves into tiny blood vessels, glomeruli and joints causing the above reaction to occur.

The reaction is usually delayed as it takes 3 to 6 hours before its occurrence after one has been exposed to the antigen than type 1 hypersensitivity which occurs immediately or after some few minutes. The extracellular immune complexes cause activation of the complement system. In autoimmune reactions the reactions last for longer periods since antigens are continuously produced. The activation of complement system leads chemotaxis which is the attraction of neutrophils, eosinophils, leukocytes and macrophages to the direction of the antigen that the body recognizes as foreign. They engulf the antigen and inflammation reactions such as swelling, redness, increased temperature at the site and pain follows as the body tries to fight the foreign body. This finally leds to death of tissue where the antigen is attacked through the process of aptosis.

Effects that can be caused by type 3 hypersensitivity reactions include skin lesions, nephritis, arthritis, occlusion of the blood flow, swelling, glomerulonephritis and rashes. It can also cause malaria symptoms such as hotness of the body, headache and nausea. These reactions have been evident in infections including hashimoto syndrome, rheumatoid arthritis, infections secondary to arthritis and lupus erythematosus.

This reaction can cause serum sickness especially evident after giving one huge quantity of soluble antigen which is unknown to the body, in therapy of diseases caused by bacteria. Its clinal features include skin rashes, hotness of the body, and skin reactions at the point of injection. Kidney which disease and brings about many clinical presentations of various infections.One should go for food sensitve testing

All people have free circulating immune complexes in their blood streams or which are outside the cells which generate response of antibodies but developing this reaction depends on availability of the antigen memory, physical properties of the antigens and antibodies and their immunological factors such as affinity, size, valence of antigen and the concentration of antibodies.

Management of this reaction varies as it depends on the clinical disorder related to the immune complex. It is advisable to stop giving the antigen that results to infection of the immune complex and anti-inflammatory drugs and those that suppress the immune system can be helpful.