MCs play a pivotal role in the host defense against pathogenic microorganisms for several reasons. First of all, MCs’ strategic position at the host–external environment interfaces, i.e., in the subepithelial layers of the skin, the respiratory system, or in the gastrointestinal and genitourinary tracts, means that they are among the first cell population to interact with invading microbes along with other innate immune cells, such as epithelial cells, and trigger a response against them. Moreover, it is well known that MCs may initiate and combat the clearance of pathogens by several mechanisms of action
[5][6][7]. MCs possess an array of bioactive substances, which affect all stages of inflammation during infection, including its initiation, maintenance, and even resolution. They include granule-associated preformed mediators (e.g., histamine, tryptase, chymase, carboxypeptidases, metalloproteinases, proteoglycans), de novo-produced eicosanoid metabolites (e.g., leukotrienes (LTs), prostaglandins, thromboxanes), as well as many newly synthesized cytokines/chemokines
[8][9][10][11][12]. MC activity against pathogens also involves the release of some antimicrobial peptides and the production of ROS. Moreover, these cells can engulf invading microbes via phagocytosis and kill them through oxidative and non-oxidative systems
[5][6]. Another described strategy used by MCs to destroy microorganisms is through extracellular traps (MCETs) composed of DNA, histones, and granule proteins
[13]. The relevance of MCETs has been documented in antibacterial, antifungal, or antiparasitic host defense
[14][15]. Following phagocytosis, MCs may process pathogen antigens for presentation through class I and II MHC molecules, which leads to the development of adaptive antimicrobial immunity
[16]. As MCs express PRRs, they may act as effectors of host defense through their ability to detect various MAMPs or endogenous DAMPs released in response to infection. The available data indicate that among PRRs expressed on MCs, there are representatives from TLRs, RLRs, and NLRs, as well as CLRs
[17]. It has been reported that MCs can recognize bacterium-associated molecules, such as lipopolysaccharide (LPS), lipoteichoic acid (LTA), or peptidoglycan (PGN) mainly through TLRs but also via some NLRs. In turn, specific TLRs and RLRs are involved in MC response to viral dsRNA, ssRNA, or envelope proteins. Among PRRs expressed on MCs, there are also molecules from the CLR group or some TLRs, which may sense different fungal components (
Figure 2)
[17]. However, little information exists concerning MC involvement in antifungal host defense, and the function of MCs in fungal infections is not precisely defined
[18][19].