Immunological Aspects of Immunodeficiency Diseases

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