Immunological Aspects of
Immunodeficiency Diseases
INTRODUCTION
The principal function of the immune system is to
prevent microbial infection. Therefore, disorders resulting in impaired
function of the immune system (immuno-deficiency) result in increased
susceptibility to infection. Immunodeficiency can arise from an intrinsic
defect of a component of the immune system (primary immunode-ficiency, or PID).
Alternatively, immuno-deficiency may be secondary to another pathological
condition, which adversely affects immune function (Table 5.1). Both primary
and secondary immunodeficien-cies result in increased susceptibility to
infection. The precise pattern of infection depends on the specific component
of the immune system that is affected. Most PIDs are caused by defects in
single genes and are hence heritable. Others may represent the consequence of
an interaction between the genetic phenotype and an environmen-tal influence,
like viral infections. Primary immunodeficiencies are rare and based on
information from national registers; these diseases are estimated to occur
between 1 in 2,000 to 1 in 10,000 live births. In con-trast, secondary
immunodeficiencies are more commonly seen in clinical practice. (See Table 5.1
for examples of secondary immunodeficiency.)
Table 5.1 Secondary Immunodeficiency
From a clinical perspective, immuno-deficiencies
can be classified into eight categories (Table 5.2). Each category has a
characteristic pattern of clinical presenta-tion (Table 5.3), which will be
elaborated on later
Table 5.2 Operational Classification of Imunodeficiency States
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