(immunology) A bodily defense reaction in response to the presence of a foreign substance (i.e. antigen) inside the body
An immune response pertains to any of the body's response to a foreign substance, such as an antigen. The response intends to protect the body from antigens, e.g. disease-causing viruses, fungi, and bacteria. A transplanted organ may also incite an immune response when it is identified as not-self.
In vertebrates, an immune response may be in the form of antibody production, induction of cell-mediated immunity, complement activation, or development of immunological tolerance. The immune response of the body helps resist disease due to the formation of humoral antibodies following an antigenic challenge (referred to as humoral immune response). Lymphocytes (such as B cells and T cells) are cells associated with the body's immune response.
A lack of an effective immune response may lead to disorders. One of them is a high-level autoimmunity where the body mistakes own substances and tissues as antigens. This condition leads to autoimmune diseases, e.g. Celiac disease, systemic lupus erythematosus, and diabetes mellitus type 1. Another is gammopathy. Gammopathy is an immune disorder characterized by an abnormal proliferation of cells producing immunoglobulins.