Hiv directly infects t-cells. why is this problematic for cell-mediated immunity?

Cell-mediated immunity is the function of phagocyte and cytotoxic T-cells. It does not involve antibodies and is specific for a particular antigen.  

In HIV infection the virus enters into the T-helper cell(CD 4 cell) and reproduces in the T helper cell. They destroy the T helper cell during this process and then enter new CD 4 cell. By this process, they reduce the number of T helper cells.

T helper cell are important for cell-mediated immunity because it releases some chemicals that activate cytotoxic T cell and phagocytes which then kill the pathogens.  

Therefore when the number of T helper cells reduces it becomes problematic for cell-mediated immunity to function properly.

The multi-cellular organism is made up of a number of cells and as they work in cooperation with another. We have the following reasons to answer the question.

Specialization of cells: It means the combination and adjustments done by various cells to perform a single and more specific function of the body. As the structure formed are called as tissues in general.

Mostly he tissues are assembled to perform the following functions;

Reception of stimulus an reaction by the body.Communication between the cells,cells junctions for material transport

Animal cell specialization includes:

Red blood cell's,Neuron cells,gametes,epithelium cells.

While animal cell specialization includes:

Root hairs on the plant body,Guard Cells,And pollen grains.

Explanation:

1) Production of materials to live and more over to survive:

Each cell inside a complex body structure(Humans and complex plant bodies)needs the optimum amount of substrate in order to create or produce further products for himself and to deliver the energy to the environment. As all the required substrate is never stored or produced by a single entity or cell but all of them are dependent upon one another, as they require the assistance in assembling the product or material for use.

2) Locomotion of the beings:

As the tissues work in corporation to maintain the level of materials in the body along with the level of energy in order to move from a certain point another.

3)Response to environment:

As the cells have receptors in it which detects and directs the body of the living being to respond to that, as the stimulus is detected by the receptor and the message is processed by the organ leading to a response.