Page 129 - Essential Haematology

Chapter 8 White cells: Granulocytes and monocytes / 115

(H 2 O 2 ) and other activated oxygen (O 2 ) species, are oxide (NO) generated through NO synthase from
generated from O 2 and reduced nicotinamide L - arginine is another mechanism by which phago-
adenine dinucleotide phosphate (NADPH). In cytes kill microbes.
neutrophils, H 2 O 2 reacts with myeloperoxidase
and intracellular halide to kill bacteria; activated

oxygen may also be involved. The non - oxidative Defects of p hagocytic c ell f unction
microbicidal mechanisms involve microbicidal pro-
Chemotaxis

teins. These may act alone (e.g. cathepsin G) or in
conjunction with H 2 O 2 (e.g. lysozyme, elastase). These defects occur in rare congenital abnormalities

They may also act with a fall in pH within phago- (e.g. ‘ lazy leucocyte ’ syndrome) and in more
cytic vacuoles into which lysosomal enzymes are common acquired abnormalities either of the envi-
released. An additional iron binding protein, lacto- ronment (e.g. corticosteroid therapy) or of the leu-
ferrin, is present in neutrophil granules and is bac- cocytes themselves (e.g. in acute or chronic myeloid
teriostatic by depriving bacteria of iron and leukaemia, myelodysplasia and the myeloprolifera-
generating free radicals (Fig. 8.7 ). Finally, nitric tive syndromes).

Bacterium
Phagocytosis

Phagosome

Primary granule
(contains acid
phosphatase,
myeloperoxidase,
esterase)

H O , activated O species Secondary (specific)
2 2
2
granule (contains
lysozyme,
elastase,
collagenase,
lactoferrin)
NEUTROPHIL
Residual body

Exocytosis

Figure 8.7 Phagocytosis and bacterial destruction. On entering the neutrophil, the bacterium is surrounded by

an invaginated surface membrane and fuses with a primary lysosome to form a phagosome. Enzymes from the
lysosome attack the bacterium. Secondary granules also fuse with the phagosomes, and new enzymes from
these granules including lactoferrin attack the organism. Various types of activated oxygen, generated by
glucose metabolism, also help to kill bacteria. Undigested residual bacterial products are excreted by
exocytosis.