**3.1 Phagocytosis**

Macrophages are one of the three professional phagocytes with other phagocytes including granulocytes (eosinophils, neutrophils, and basophils) and dendritic cells (DC). Phagocytosis is the process that microorganisms entering the host and recognised by phagocytes and incorporated and destroyed. This process starts after the interaction with pathogen-specific receptors (usually pathogen-specific sugar or lipid structures) on phagocytes and the surface molecular on pathogens. Typical phagocyte receptors are dectin-1 and mannose receptor (CD206), and both are the family of members of c-type lectin. Dectin-1 expressed on macrophages and neutrophils connects with glucose polymers on the cell walls of fungus. On the other hand, CD206 expressed on macrophages and DCs connects with variety of ligands on fungus, bacteria, and virus. Generally, macrophages exist in all of tissues and monitor potential pathogens with amoebic motility. Most of macrophages are strategically placed where microbes invade or debris accumulate [7].

After starting interaction with pathogens, phagocytic plasma membrane in macrophages engulfs pathogens into phagosomes, large membrane-enclosed endocytic vesicles (endosomes). Phagosomes enclose pathogens, merged with lysosomes containing antimicrobial peptides and enzymes, and form phagolysosomes. Toxic peroxides like superoxide radicals in phagolysosomes kill and digest pathogens after acidification and enzymic processes. Macrophages ultimately digest over 100 bacteria through digestive compounds in their lifetime. However, some bacteria have resistant properties to these digestive methods. Mycobacterium tuberculosis survives within the macrophages through inhibiting the fusion to phagosomes. To reproduce themselves, Salmonella enterica serovar Typhi induces phagocytosis to incorporate into macrophages, inhibits lysosomal digestion, and triggers apoptosis of macrophages. Furthermore, leishmaniasis causes Leishmania parasitises in macrophages.
