The human immunodeficiency virus (HIV) that causes the disease known as aids selectively infects helper T cells (CD4+).
This retrovirus also infects macrophages and dendritic cells. When CD4+ T cell numbers decrease below a critical level (due to the killing of this cells with different mechanisms), cell-mediated immunity is lost. As a result, the body becomes progressively more susceptible to infections, leading to the development of AIDS.
<span> HIV can be transmitted only via body fluids like blood, semen, pre-seminal fluid, rectal fluids, vaginal fluids, and breast milk, which means that people usually get or transmit HIV through sexual behaviours and use of the needle. For HIV infection, these fluids must come in direct contact with a mucous membrane or damaged tissue. Another way is to be directly injected into the bloodstream (from a needle for example).</span>
Thermocline - <span>a steep temperature gradient in a body of water, that is marked by a layer above and below at which the water is at different temperatures.
halocline - </span><span> a subtype of chemocline caused by a strong, vertical salinity gradient within a body of water.
pycnocline - </span><span>a layer in an ocean or other body of water in which water density increases rapidly with depth.</span>
The blood group of AB because they are have both A and B glycoproteins on the surface of the cell
