Oxidative burst

Neutrophils (& monocytes) produce hydrogen peroxide (through superoxide production) to kill phagocytosed bacteria. 

2O₂ + NADPH —> 2O₂^•– + NADP⁺ + H⁺

This reaction is catalaysed by NADPH oxidase. A series of reactions then generates hydrogen peroxide from this superoxide radical, and finally hypochlorous acid.

In vitro, this reaction can be visualised by Dihydrorhodamine (DHR), which is oxidised by H2O2 from normal, stimulated neurophils to give fluorescence (in the FITC channel). EDTA/ heparin blood must be used within 2 hours of collection, in room temparature all the time.

Gating neutrophils, lymphocytes and monocytes from whole blood

Before and after stimulation; note presence of DHR peak ('oxidative burst') in neutrophils and monocytes, and not in lymphocytes

The lack of superoxide produces a (weirdly named) disease.

Chronic granulomatous disease

Well, this has got (almost) nothing to do with granulomas (maybe a little, indrectly). This is a defect in several components of NADPH oxidase, resulting in inability to produce hydrogen peroxide. An X linked form (75%) & an autosomal recessive form (25%) occur.

Agent

XR: Mutation in phagocyte NAPH-O complex due to defect in gene for gp91phox.

AR: Defects in genes p47,67,22 phox or RAC2

It manifests as recurrent pyogenic infection with catalase +ve organisms.

Pathology

Three scenarios:

1. Normal neutrophils accumulate H2O2 in the phagosome containing ingested bacterium → MPO (myeloperoxidase) is delivered to the phagosome by degranulation, → H2O2 acts as a substrate for MPO to oxidize halide to hypochlorous acid and chloramines, which then kill the microbes. The quantity of hydrogen peroxide produced by normal neutrophils is sufficient to exceed the capacity of catalase, a hydrogen peroxide-catabolizing enzyme of many aerobic microorganisms.

2. When catalase +ve organisms such as E. coli gain entry into the CGD neutrophils, they are not exposed to hydrogen peroxide because the neutrophils do not produce it, and the hydrogen peroxide generated by microbes themselves is destroyed by their own catalase. Thus catalase-positive microbes, such as E. coli, can survive within the phagosome of the CGD neutrophil.

3. When CGD neutrophils ingest catalase negative organisms such streptococci or pneumococci, the organisms generate enough hydrogen peroxide to result in a microbicidal effect; i.e. they are killed by their own hydrogen peroxide.

(Ref: Williams, Hematology)

Thus there is a preponderane by recurrent infections by Catalse positive organisms.

CGD; note the lack of oxidative burst in stimulated neutrophils