A 9 year old girl receives an intradermal tuberculin injection and later develops an indurated, erythematous papule 12 mm in diameter. This reaction is an example of which of the following?
Antibody-dependent cell-mediated cytotoxicity
Local anaphylaxis
T-cell mediated cytotoxicity
Type IV hypersensitivity
The tuberculin reaction is an example of delayed-type hypersensitivity (a form of Type IV hypersensitivity) in which the bulk of the tissue damage is done by macrophages that are stimulated by a few previously sensitized CD4+ memory T-cells recognizing antigens presented by the macrophages. In contrast, in T-cell mediated cytotoxicity ( another form of Type IV sensitivity) the damage is done by CD8+ cytotoxic T-cells that recognize "foreign" cell surface antigens and directly lyse targeted cells. Antibody-dependent cell-mediated cytotoxicity reactions (a form of Type II hypersensitivity) involves cells coated with a thin layer of antibody that triggers attack by cells (monocytes, neutrophils, eosinophils, and natural killer cells) that can bind to Fc receptors. Local anaphylaxis (a form of Type I hypersensitivity) is due to the release of vasoactive substances by mast cells and basophils stimulated by memory (CD4+) T-cells reacting to antigen. Ref: Ray C.G., Ryan K.J. (2010). Chapter 27. Mycobacteria. In C.G. Ray, K.J. Ryan (Eds), Sherris Medical Microbiology, 5e.