Final answer:
Second-degree immune-mediated Type II hypersensitivity involves IgG and IgM antibodies that target antigens on cell surfaces, triggering an immune response that damages the cells. This can occur in autoimmune diseases, mismatched blood transfusions, and when the immune system mistakes the body's cells for foreign invaders due to molecular mimicry, as seen in rheumatic fever and Type 1 diabetes.
Step-by-step explanation:
Type II Cytotoxic Hypersensitivity
Second-degree immune-mediated cytotoxic hypersensitivity (Type II hypersensitivity) is associated with various autoimmune conditions where IgG and IgM antibodies target antigens present on cell surfaces or basement membranes. This can lead to cellular damage through activation of complement proteins causing lysis or through antibody-dependent cell-mediated cytotoxicity (ADCC) involving cytotoxic T cells. Type II hypersensitivity responses can be observed in conditions such as mismatched blood transfusions, blood compatibility diseases like erythroblastosis fetalis, and in autoimmune diseases where antibodies may mistake the body's cells as foreign due to molecular mimicry.
For example, an autoimmune response known as rheumatic fever can arise after a streptococcal infection when the antibodies or T cells react with heart muscle antigens that share structural similarities to Streptococcus pyogenes. Another instance is insulin-dependent diabetes mellitus, characterized by a destructive inflammatory response against the insulin-producing cells of the pancreas.