The immune system is constantly alert to recognise and neutralise invading microorganisms and foreign molecules. To cope with a large spectrum of substances and organisms, nature has developed highly sophisticated response systems. Innate immunity can generate a fast but usually nonspecific response. Adaptive immunity facilitates specific recognition. The recognition components – antigens, B- and T-cell receptors, and major histocompatibility complexes – of the adaptive immunity originate from gene rearrangements, which produce countless combinations of recognition sites. Together the immune system is capable of protecting the body from most microorganisms. When components of the machinery are mutated the affected individuals suffer from immunodeficiencies. Primary immunodeficiencies can arise from numerous mutated genes, which leads to a large number of very different immunodeficiencies, which require different therapeutic approaches. The disorders vary greatly in regard to symptoms, infection-causing organisms, genotype, phenotype, and severity of the disease. The genetic background and disease-causing mutations, symptoms, and therapy are discussed for a number of well-characterised primary immunodeficiencies.

INTRODUCTION

Adaptive immune mechanisms recognise and neutralise foreign molecules or microorganisms in a specific manner. B and T lymphocytes can respond selectively to thousands of nonself materials. Adaptation is further acquired with memory of previous infections. The other arm of the immune system, native (innate) immunity is able to respond almost immediately to potentially infectious agents. The major components of innate immunity are natural killer cells, phagocytes, and the complement system. Innate immunity has only a limited specificity to distinguish one microbe from another.