lifeisbeautiful: 2011

Suspicion of an immune disorder should trigger testing of immune function. For example, patients with chronic, recurrent, or unusual infections, may have an immune deficiency. Alternatively, persons who consistently present with localized edema and itching following contact with an object in their environment may be suspected of having a hypersensitivity response to an antigen associated with that object.

Defects in the humoral arm usually result in a patient having difficulty clearing encapsulated bacteria from the bloodstream, which may result in life-threatening infections. The bacteria seen in these immunocompromised states are mostly Streptococcus pneumoniae, Haemophilus influenza, and Neissera meningitidis. Defects in humoral immunity may be primary and often present since birth, or they may be acquired. They are quite diverse and include such diseases as selective IgA defiency, common varible immune defiency in which immunoglobin levels are depressed, and the acquired immune defiency state caused by human immunodeficiency virus (HIV)-1 in which immunoglobulin levels are elevated but disordered secondary to immune dysregulation and are therefore ineffective. It is important to realize that patients with asplenia, whether secondary to a functional defect or frank absence, are also at greatly increased risk of overwhelming bacteremia, especially with encapsulated bacteria and subsequent life-threatening sepsis syndrome.

The cellular componet fights viral infections and performs immune surveillance and may prevent or delay malignancy. The best example for the role of T lymphocytes is in advanced HIV-1 disease, acquired immune deficiency syndrome (AIDS), when CD4⁺ T cells are severely depleted. Such patients develop opportunistic infections with fungi such as cryptococcus, viruses such as CMV and adenovirus, and mycobacteria such as Mycobacterium tuberculosis and Mycobacterium avium-intracellulare complex.