CTLs can kill cells infected with viruses or intracellular bacteria. They also can kill cancerous cells. How might an infected or cancerous cell evade immune control by CTLs? a. Increased expression of MHC class II molecules.
b. Increased expression of MHC class I molecules.
c. Decreased expression of MHC class I molecules.

The correct option is C (Decreased expression of MHC class I molecules.)

Explanation:

The lymphocyte is the major type of white blood cells which is divided into two:

--> B Lymphocyte and

--> T Lymphocyte

The T Lymphocyte is further divided into two namely:

--> T helper cells and

--> Cytotoxic T Lymphocyte (CTL)

The T lymphocyte cells recognize a non self target such as a pathogen only after pathogen has been processed and it's antigen presented in combination with a complex known as the Major histocompatibility Complex ( MHC). There are two types of MHC which includes Type 1 and Type 2 MHC.

The cytotoxic T Lymphocyte only recognize antigen combined with Class 1 MHC.

Some virus mechanism of action, while invading some target cells, is to reduce the normal levels of surface class 1 MHC in order to evade or escape the immune control by cytotoxic T Lymphocyte. Therefore the correct statement is decreased expression of MHC class I molecules.

it provides an alternative energy pathway for the reaction to proceed.

a catalyst is a substance that speeds up the rate of a chemical reaction but is not consumed during the course of the reaction.

catalysts increase the rate of reaction without being used up. they do this by lowering the activation energy needed. with a catalyst, more collisions result in a reaction, so the rate of reaction increases. different reactions need different catalysts.

a catalyst works by providing an alternative reaction pathway to the reaction product. the rate of the reaction is increased as this alternative route has a lower activation energy than the reaction route not mediated by the catalyst.