Questions: Self antigens a proteln chalns MHC II molecules MHCI molecules

The answer is the third one: MHC I molecules.

Explanation for each option:

1. Protein chains: This is incorrect because while self-antigens can be proteins, the term "protein chains" is too broad and does not specifically refer to the molecules involved in presenting self-antigens.
2. MHC II molecules: This is incorrect because MHC II molecules are primarily involved in presenting antigens to helper T cells and are typically associated with exogenous antigens, not self-antigens.
3. MHC I molecules: This is correct because MHC I molecules present self-antigens (as well as endogenous antigens) to cytotoxic T cells, which is a key part of the immune system's ability to recognize and respond to infected or abnormal cells.
4. MHC I molecules: This is a repeat of the correct answer.

Summary: Self-antigens are presented by MHC I molecules, which play a crucial role in the immune system's ability to monitor and respond to cells within the body.