Sechenov School
Home › Microbiology › Antifungal Immunity

Antifungal Immunity

For medical students2 min readUpdated 2026-10-10

Antifungal immunity is a complex of host defense reactions aimed at recognizing, neutralizing, and destroying pathogenic fungi. Protection is primarily driven by innate resistance factors and cell-mediated adaptive immunity, which respond to specific structural components of the pathogen.

Main targetMultilayered fungal cell wall (glucans, chitin, mannans).
ReceptorsPattern-recognition receptors: TLR2, TLR4, and dectin-1.
Controlling factorNormal microflora actively competes with fungi for ecological niches.
Basis of protectionT-cell adaptive immunity is more important than humoral immunity.

Pathogen Structure as an Immune Target

The logic of the antifungal response is fundamentally based on the structure of the pathogen. Fungi differ significantly from bacteria by possessing a thick, complex, multilayered cell wall.

This structure serves as the primary target for recognition by host defense systems. The cell wall consists of:

Innate Immunity: The First Line of Defense

Innate immunity bears the initial brunt of contact with fungal agents. Defense at this stage is carried out through three main mechanisms:

  1. Barrier factors. The physical integrity of the skin and mucous membranes prevents invasion. Additionally, sebaceous and sweat gland secretions contain natural antimicrobial peptides that are detrimental to micromycetes.
  2. Competitive defense. Healthy normal microflora acts as a powerful antagonist. Bacteria compete with fungi for nutrients and ecological niches, strictly suppressing their overgrowth.
  3. Receptor recognition. If a fungus breaches these barriers, innate immune cells come into play. They use specialized receptors (primarily TLR2, TLR4, and dectin-1) to recognize fungal cell wall polysaccharides and trigger an inflammatory cascade.

Adaptive Immunity and Tissue Responses

If innate mechanisms fail, adaptive immunity is activated. In mycoses, T-cell immunity plays a leading role. The humoral response (production of IgM and IgG antibodies) is of secondary importance and cannot independently ensure complete clearance of fungi from the organism.

A characteristic pathomorphological pattern unfolds at the site of inflammation:

Clinical and Immunological Features of Mycoses

Fungal infections (especially opportunistic ones) rarely affect completely healthy individuals. They manifest against a background of immunodeficiencies or following prolonged antibiotic therapy when the protective normal microflora has been depleted.

The infectious process is always accompanied by the development of delayed-type hypersensitivity (DTH). However, fungi can also trigger allergic reactions (immediate-type hypersensitivity — ITH).

Respiratory sensitization most commonly occurs upon inhaling microscopic fragments of fungi of the genera Aspergillus, Penicillium, Mucor, or Fusarium. The body begins to synthesize specific IgE antibodies, leading to severe allergic conditions (e.g., bronchial asthma).

In clinical practice, specific skin tests with fungal antigens are widely used to diagnose active infection (DTH) or allergy (ITH).

Frequently asked questions

Which cells perform phagocytosis during fungal infections?

Phagocytosis during fungal infections is performed predominantly by macrophages and neutrophils.

  • Macrophages recognize fungi via lectin receptors (mannose receptor, DC-SIGN, dectin-1) and engulf them (e.g., alveolar macrophages phagocytose spores in coccidioidomycosis).
  • Neutrophils provide phagocytosis and intracellular digestion of pathogens (e.g., in sporotrichosis).
  • Monocytes also express receptors for pathogen recognition and endocytosis.
What cytokines are released upon activation of T-cell antifungal immunity?

Interferon-gamma (IFN-$\gamma$) is released upon activation of T-cell antifungal immunity. During the immune response, T lymphocytes recognize fungal cell wall antigens and specific heat shock proteins, after which they secrete this cytokine. The release of interferon-gamma activates macrophages, subsequently leading to the effective intracellular destruction of engulfed fungi.

What immune evasion mechanisms do pathogenic fungi use?

Pathogenic fungi employ several mechanisms to evade the immune response and destruction by phagocytes.

  • Blocking phagosomal-lysosomal fusion — this mechanism has been described for the causative agent of coccidioidomycosis.
  • Intracellular survival — Histoplasma species are facultative intracellular parasites; they are engulfed by macrophages, replicate within phagolysosomes, and subsequently cause macrophage destruction.
  • Capsule formation — in Cryptococcus species, the capsule inhibits phagocytosis.
Why do candidiasis and other mycoses frequently occur after a course of antibiotics?

Antibiotics destroy the normal bacterial microflora, which normally competes with fungi for nutrients. Deprived of competitors, fungi begin to multiply uncontrollably.

Which arm of immunity is more important for fighting fungi: cell-mediated or humoral?

T-cell immunity plays the leading role. Humoral immunity (IgM, IgG antibodies) is of secondary importance in mycoses.

Through which receptors does the body recognize fungi?

The primary 'sensors' of the thick fungal cell wall components are innate immune receptors: TLR2, TLR4, and dectin-1.

Which fungi most commonly cause respiratory allergies?

Respiratory sensitization with IgE production is most commonly caused by fragments of mold fungi of the genera Aspergillus, Penicillium, Mucor, and Fusarium.

Go deeper

More topics in Microbiology

Influenza Treatment and PreventionPolyomavirusesHIV Treatment and PreventionPneumocystosis (Pneumocystis jirovecii)Immunological Period of MicrobiologyHuman Normal MicrofloraSystemic VasculitidesEcological and Epidemiological Classification of InfectionsPhysicochemical Diagnostic Methods in MicrobiologyPenicillium and Aspergillus Toxicosis: USMLE ReviewBacterial Cell WallDNA Replication in BacteriaMicrobiology →