Question

APCs stimulate CD4 T cells by way of MHC receptors and what costimulatory receptors? Which of these is "tricked" by tumor cells?

Answer 1

APCs activate CD4+ T cells via MHC II receptors and require additional signals from costimulatory receptors like CD28 and B7. Tumor cells can evade the immune response by manipulating these signaling pathways, specifically by expressing PD-L1 which binds to PD-1 on T cells and inhibits their activity.

Step-by-step explanation:

Antigen-presenting cells (APCs) play a critical role in stimulating CD4+ T cells by way of Major Histocompatibility Complex (MHC) class II receptors. However, to achieve full activation, CD4+ T cells require additional signals from costimulatory receptors.

One of the primary costimulatory signals comes from the interaction between CD28 on the T cell and B7 molecules (CD80/CD86) on the APC. Conversely, CD8+ T cells become cytotoxic T lymphocytes (CTLs) when they are stimulated by antigens presented on MHC class I molecules.

Tumor cells can sometimes 'trick' the immune system by downregulating these MHC molecules or by expressing checkpoint molecules like PD-L1 that bind to PD-1 on T cells, providing an inhibitory signal that effectively turns off the immune response against the tumor.

This evasion strategy allows tumor cells to grow without being attacked by the body's immune system, leading to the development and progression of cancer.