Apoptosis is a programmed cell death process in which cells undergo specific changes to eliminate damaged or unnecessary cells

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The first step of thymic selection occurs in the cortex of the thymus and involves the development of a functional T-cell receptor that is required for activation by APCs. Thymocytes with defective TCRs are removed by negative selection through the induction of apoptosis.

The First Step of Thymic Selection

The second step of thymic selection also occurs in the cortex and involves the positive selection of thymocytes that will interact appropriately with MHC molecules. Thymocytes that interact appropriately with MHC molecules receive a positive stimulation that moves them through the process of maturation, and thymocytes that do not interact appropriately  are eliminated by apoptosis

The Second Step of Thymic Selection 

The third step of thymic selection occurs in the cortex and medulla. It involves negative selection to remove self-reacting thymocytes by apoptosis. This step is also referred to as central tolerance because it prevents self-reacting T cells from reaching the bloodstream and potentially causing autoimmune disease.

The Third Step of Thymic Selection 

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Microbiology covers the scope and sequence requirements for a single-semester microbiology course for non-majors. The book presents the core concepts of microbiology with a focus on applications for careers in allied health. The pedagogical features of the text make the material interesting and accessible while maintaining the career-application focus and scientific rigor inherent in the subject matter. Microbiology’s art program enhances students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs.

Microbiology is produced through a collaborative publishing agreement between OpenStax and the American Society for Microbiology Press. The book aligns with the curriculum guidelines of the American Society for Microbiology.

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