Immunodeficiency - Leukocyte Function

It has been found that the chemotaxis, phagocytosis, and other anti-foreign microorganism actions of leukocytes are reduced (Fabris et al, 1993). Licastro et al (1993b, 1994) investigated the ability of DS neutrophils to produce chemically active molecules, such as the superoxide anion, when stimulated. They observed that chemical activity was low before supplementation but after zinc therapy neutrophil reaction to a stimulus was normalised. The authors point out that protein kinase C is believed to play an important role in the activation of human neutrophils, including superoxide generation, and that the activity of protein kinase C is regulated by zinc ions. Possibly the actual fault is an impaired activation of protein kinase C because of a poor supply of zinc ion. Rates of infection amongst the subjects were found to decrease with supplementation, but the same problems with this data apply as previously discussed, especially the compilation of a record of each child’s infection history for the year preceding the experiment from what the parents recalled.

Neutrophil chemotaxis was also found to be reduced in DS patients by about 30%, but normalised after zinc therapy (Björkstén et al, 1980). Björkstén et al relate zinc enhancement of neutrophil activity to possible membrane phenomena and also mention intracellular activity, as leukocyte locomotion is very complex. Licastro et al (1993) also followed up their subjects a year after ceasing zinc therapy and found that neutrophil activity had dropped again, supporting their assumption that zinc had improved their functioning. Unfortunately Björkstén did not follow up his subjects so a similar comparison is not available.

That zinc supplementation may improve neutrophil deadliness is very important in attempting to understand how to reduce the incidence of infection in DS people. Further investigation to expand understanding in this area could prove very fruitful, including investigation into the role of protein kinase C and its relationship with zinc.