Explanation: 👍 The correct answer is E. The vignette describes a child who is suffering from small bowel intussusception after a recent GI infection. GI infections cause reactive hyperplasia of Peyer's patches which can then serve as lead point for intussusception. Peyer patches are small masses of lymphatic tissue whose function is to survey intestinal bacterial populations and arm the body against overgrowth of pathogenic bacteria. M cells contained within Peyer patches take up antigens and present them to B cells. B cells then form germinal centers and, following CD40L stimulation from T cells, class switch to IgA and differentiate into plasma cells.
👎 A is not correct. Active immunity refers to the immunity that develops in the host due to production of antibodies by "memory" B and T cells in response to a foreign antigen following infection.
👎 B is not correct. Cell-mediated immunity involves phagocytes, cytotoxic T cells and cytokines produced in response to a foreign antigen following infection. Peyer's patches primarily provide defense mechanism against GI luminal bacteria via antibody-mediated rather than cell-mediated immunity.
👎 C is not correct. Activation of the complement cascade in response to the presence of bacteria is an arm of the innate immune response. Peyer's patches do not primarily act by activation of complement.
👎 D is not correct. This describes an autoimmune response, in which the body is unable to discern between self-antigens and foreign antigens. Though it is an important immune function in the body as a whole, it is not the primary function of Peyer's patches.