Tc cells recognize epitopes only when the latter are held by:
a. MHC proteins
b. B cells
c. Interleukin 2
d. Granzyme

Verified step by step guidance

1. Understand that Tc cells, or cytotoxic T cells, recognize antigens in a very specific way, which involves the presentation of epitopes.
2. Recall that epitopes are small parts of antigens that are recognized by immune cells, but Tc cells require these epitopes to be presented on the surface of other cells.
3. Identify the molecules responsible for presenting epitopes to Tc cells. These are the Major Histocompatibility Complex (MHC) proteins, specifically MHC class I molecules.
4. Recognize that MHC proteins bind to epitopes and display them on the surface of infected or abnormal cells, allowing Tc cells to detect and respond to these cells.
5. Conclude that Tc cells recognize epitopes only when they are held by MHC proteins, making option (a) the correct choice.

Key Concepts

T Cell Receptors and Epitope Recognition

T cell receptors (TCRs) on cytotoxic T cells recognize specific peptide fragments called epitopes. However, this recognition only occurs when epitopes are presented on the surface of cells bound to major histocompatibility complex (MHC) molecules, enabling the immune system to detect infected or abnormal cells.

Major Histocompatibility Complex (MHC) Proteins

MHC proteins are cell surface molecules that display peptide fragments derived from pathogens or abnormal proteins. Class I MHC molecules present epitopes to cytotoxic T cells (Tc cells), which is essential for the immune response against intracellular infections and cancerous cells.

Role of Cytotoxic T Cells (Tc Cells)

Cytotoxic T cells are immune cells that kill infected or abnormal cells by recognizing epitopes presented by MHC class I molecules. This recognition triggers Tc cells to release cytotoxic substances, such as perforin and granzymes, to induce apoptosis in the target cell.