What are CD4 lymphocytes?

Hint: Lymphocytes are a type of white blood cells responsible for adaptive or acquired immunity that is present in the blood and lymph of our body. They are agranulocytes. They are categorized into three types of lymphocytes, i.e., B-lymphocytes, T-lymphocytes and Natural killer cells (NK cells).

Complete answer:
CD4 cells are glycoproteins present on the immune cells’ surface of cells like monocytes, T helper cells, monocytes, macrophages and dendritic cells. CD4T cells are pivotal and play a major role in immunity by fighting infections and serving as critical defensive structures of the immune system. HIV attacks these CD4 cells. The strength of an infected person’s immune system can be determined by CD4 count. CD4 T-cells are considered helper cells as they stimulate the immune system to respond to infections rather than neutralizing infections.

For HIV to be able to infect host cells, it has to multiply, for this CD4 cells are its prime targets. HIV attaches to these CD4 cells during infections unloading its genetic content so as to alter the genetic coding of the host to finally generate HIV virions. In the process, the CD4 cells of the host are destroyed and more and more viral particles are generated using the host's machinery. With time immunity diminishes and reaches a stage where the body is susceptible to opportunistic infections.

Note: Lymphocytes play a major role in adaptive immunity. Humoral immunity is maintained by B cells and cell-mediated immunity is maintained by T cells. antibodies are secreted by B cells which are transported by blood whereas T cells can migrate to the target tissues and act locally.

The acquired immune response is pathogen-specific. Once acquired, it is stored in the memory cell, so that when the infection is repeated, it triggers a highly intensified secondary response.