An increased susceptibility to respiratory infections as manifested by a history of recurrent respiratory infections.

A lasting absence of total IgG and total IgA and total IgM in the blood circulation, whereby at most trace quantities can be measured.

Failure of the immune system to protect the body adequately from infection, due to the absence or insufficiency of some component process or substance.

An decreased number of circulating monocytes.

An opportunistic disease caused by invasion of unicellular fungus Pneumocystis jirovecii. Transmission of P. jirovecii cysts takes place through the airborne route, and usually, its presence in lungs is asymptomatic. However, people with impaired immunity, especially those with CD4+ T cell count below 200/microliter, are still at risk of the development of Pneumocystis pneumonia due to P. jirovecii invasion. Symptoms induced by this disease are not specific

An abnormally decreased level of immunoglobulin in blood.

Impaired proliferation and expansion of a T cell population following activation by an antigenic stimulus.

An abnormally decreased proportion of CD4-positive, CD25-positive, alpha-beta regulatory T cells in circulation, relative to another population of cells.