Question

A healthy 20-year-old male Marine receives a tetanus immunization booster as part of routine preparation prior to an assignment. After 4 hours, he complains of pain and massive swelling at the site of injection. The medical officer examining him the next day observes the formation of an ulcer at the site.

Question
What is the most likely mechanism behind this reaction?

Accumulation of mononuclear cells at the site of antigen injection
Antigen capture by Langerhans' cells in the epidermis
Local fixation of complement performed by circulating antibodies
Local release of histamine
Predominant synthesis of IgM antibodies

Answer 1

The most likely mechanism behind this reaction is delayed hypersensitivity, which is a cell-mediated immune response occurring after secondary exposure to an antigen.

Step-by-step explanation:

The most likely mechanism behind this reaction is delayed hypersensitivity, which is a cell-mediated immune response that occurs approximately one to two days after secondary exposure to an antigen.

In this case, the tetanus immunization booster is the antigen. Delayed hypersensitivity involves the T₁ cytokine-mediated inflammatory response and may manifest as local tissue lesions or contact dermatitis.

The reaction at the injection site, including pain, swelling, and the formation of an ulcer, is characteristic of delayed hypersensitivity.