Question

choose all that are possible causes for a lack of self tolerance. lack of t cells alteration of self antigens abnormal exposure to self antigens cross reactivity between similar antigens severe combined immunodeficiency

Explanation:

• Alteration of self antigens: When self - antigens change (e.g., due to mutation, chemical modification), the immune system may no longer recognize them as "self", leading to an immune response against the altered self - antigens.
• Abnormal exposure to self antigens: Some self - antigens are normally sequestered (e.g., in the eye, testes). If there is injury or other mechanisms that expose these sequestered antigens to the immune system, the immune system may mount an attack as it perceives them as foreign.
• Cross reactivity between similar antigens: If a foreign antigen (e.g., from a pathogen) has a similar structure to a self - antigen, the immune response generated against the foreign antigen can also react with the self - antigen.

• Lack of T cells: T cells (especially regulatory T cells) play a role in maintaining self - tolerance. But a complete lack of T cells (as in severe combined immunodeficiency where both T and B cells are affected) leads to a general immunodeficiency rather than a specific lack of self - tolerance. Severe combined immunodeficiency is a more global immune defect rather than a cause specifically related to the breakdown of self - tolerance mechanisms.

Answer:

• Alteration of self antigens
• Abnormal exposure to self antigens
• Cross reactivity between similar antigens