Immunology of Invasive Fungal Infections

Abstract

For most of the twentieth century, clinically apparent, invasive systemic mycoses have been frequently recognized and well known to physicians practicing within endemic areas. Until the last two decades the discovery of a patient with an invasive systemic mycosis outside an endemic area was a rare enough entity to incite animated conversations between interested clinicians. This relative rarity of clinical disease contrasted with the fact that potentially pathogenic fungi are widespread in nature. Human contact with these organisms must be common. In the case of some of these fungi, exposure normally leads to inapparent or mild, self-limited infections (e. g., Histoplasma capsulatum, Coccidioides immitis). For other pathogenic fungi there is at least circumstantial evidence that such subclinical infections occur frequently (e. g., Paracoccidioides brasiliensis, Cryptococcus neoformans). With some mycoses, invasive disease occurs almost exclusively in patients with specific alterations in local or systemic host defense mechanisms (e. g., Absidia, Rhizopus, or Mucor species causing mucormycosis). In recent years systemic mycoses have been recognized with greatly increased frequency. In part this is because immunosuppressive ther- apy for other diseases has become commonplace. In addition, there have been major advances in using immunological markers for diagnosis and estimating prognosis of mycoses. In other words, the nature of the immune response that occurs in an individual patient after exposure to fungi is critical in determining the outcome and extent of infection, and also provides parameters useful in diagnosis and in following the course of therapy. This chapter will review the immune response to several agents which cause invasive mycoses in man (excluding Candida and Aspergillus, which are covered in other chapters).