**2. Professional phagocytes**

Neutrophils and macrophages both have a key role in innate immunity because they recognize ingest and destroy pathogens without the assistance of the adaptive immune response. Usually macrophages are the first to encounter microbes in the tissues but are soon replaced but a large number of neutrophils to sites of infection [1].

Our bodies are made of strong epithelial layers of defense however some pathogens have evolved strategies to penetrate these defense and therefore epithelia can be disrupted by wound, insect bites or abrasions that may lead to entry of pathogens.

Phagocytosis is fundamental for host defense against invading pathogens and contribute to the immune and inflammatory response. Phagocytosis is done majorly in specialized cells in multicellular organisms and is facilitated by a number of cells called phagocytes preferably professional phagocytes and these include neutrophils, macrophages, monocytes, dendritic cells. In this process a cell uses its plasma membrane to engulf a large particle giving rise to an internal compartment called the phagocytosis. Microbes are recognized by phagocytes that have a number of receptors on their surfaces which directly recognize conserved molecules on the microbe surfaces called PAMPs. This particulate matter must be opsonized (coated) with IgG, complement fragments C3b or iC3b, fibrinoctin or other proteins before being recognized and engulfed by PMNs. This process is essential for tissue balance and involve several steps that include particle recognition, particle ingestion early phagosome formation, late phagosome formation and phagolysosome formation [2].

### **3. Receptors involved in phagocytosis**

Variety of ligands can be recognized by most phagocytic cells, with their efficient recognition requiring a great number of receptor types with distinct selectivity. Multiple receptor types are co expressed and this helps display a diverse array of adherent opsonins, some phagocytic receptors engaged in the process of phagocytosis may not be phagocytic receptors. The most commonly engaged receptors are listed in the **Table 1** [13]. Macrophages recognize and identify the phagocytic targets using this array of receptors that are normally displayed on the plasma membrane of microbes.

This happens through a coordinated signaling cascade that is initiated once a phagocytic receptor binds its ligand [14].

The recognition and identification were the first known functions of phagocytosis.


**Table 1.**

*Shows human phagocytic receptors found on phagocytes.*
