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Phagocytosis

Phagocytosis process is the first line of immunological defense to engulf and digest foreign antigens and process them for presentation to  its specific cells.

It is mediated by two different cell types i.e. circulatory phagocytes i.e. neutrophils and tissue phagocytes i.e. macrophages, which are derived from monocytes and populate tissues like lung, liver, kidney, spleen, brain and lymph nodes.

Neutrophilic phagocytes mainly act against pyogenic bacteria, while macrophages are predominantly involved in killing of intracellular organisms e.g. mycobacteria, toxoplasma etc. and inducing T-cell mediated immune response.

Phagocytosis process of a foreign element involves a cascade of activity, including Recognition of the invader as a non-self antigen, Chemotaxis i.e. recruitment of more phagocytic cells, mobilized from other sites as well as bone marrow, Phagocytosis process i.e. attachment and entrapment of antigen within phagocytes by a process of vacuolization, and Microbiocidal activity within the phagocytes to eliminate entrapped pathogens by various oxidative, hydrolytic or defenses mediated systems.

Phagocytosis

Although non-specific Phagocytosis process is facilitated by specific antibodies on phagocytes, which act as ligands to bind them with pathogen, and opsonins in serum – products of complement system, which neutralize anti-phagocytic factors on bacterial cells.

Phagocytosis include quantitative phagocytic cell deficiency e.g. neutropenia, or qualitative functional defects of these cells.

Clinical features

Clinically, these defects usually present with recurrent mucus membrane infections e.g. gingivitis; or superficial/deep abscesses due to pyogenic or gram -ye organisms.

Absence of pus formation despite severe infection is a hallmark of leukocyte migration defect. Other indicators of phagocytic disorders are poor wound healing and delayed separation of umbilical cord in newborn.

Diagnosis

Diagnosis of Phagocytosis depends on abnormal neutrophil count and morphology, Nitroblue tetrazolium test (NBT) for intracellular phagocytic capacity and c) in vitro tests for neutrophil functions like chemotaxis, phagocytosis and microbiocidal activity.

Management of Phagocytosis include long -term cotrimexazole prophylaxis or recombinant interferon (IFN-y) therapy, c) colony stimulating factors (G-CSF, GM-CSF) in leukopenic states and stem cell transplantation in selected cases.

Some important inherited Phagocytosis are as follows —

Chronic granulomatous disease of childhood (CGDC) is an X-linked or autosomal recessive disorder, characterized by defective intracellular killing of microbes within phagocytes, due to abnormal oxidative metabolic responses.

Most cases present in early infancy with a) serious, recurrent or persistent infections, b) pen-oral Anal eczema and c) hepatosplenomegaly.

Chediak-Higashi syndrome is an autosomal recessive Phagocytosis of defective chemotaxis, degranulation and intracellular killing.

Apart from recurrent infections in early childhood, these cases are associated with oculocutaneous albinism, neurological abnormalities e.g. mental retardation, pyramidal!cerebellar signs, peripheral neuropathy etc., and c) neutrophils with giant cytoplasmic granules.

Cyclic neutropenia is an autosomal dominant disorder, characterized by cyclical fluctuations in peripheral neutrophil counts between normal and neutropenic values (<500/mm3) with mean oscillatory period of 21 days.

During neutropenic phase, child may suffer from mild problems e.g. oral ulcers, pharyngitis, lymphadenopathy etc. or more serious infections e.g. pneumonia. Cycles become less noticeable with advancing age, changing into chronic neutropenia.

Hyper 1gB syndrome (Jobê syndrome) is a rare case of Phagocytosis of chemotaxis and opsonization, characterized by elevated IgE levels (>2000 mg/dl), eosinophilia, recurrent staphylococcal abscesses of skin/deeper tissues and atopic dermatitis.

Lazy leukocyte syndrome is a rare case of Phagocytosis of chemotaxis and neutrophil migration from bone marrow, despite adequate bone marrow reserves.

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