Letter: Selective inhibition of phagocytic activity of rabbit alveolar macrophages by cystic fibrosis serum.

As far as rabbit alveolar macrophages are concerned, the concentration of homozygous 
CF serum used in our experiments was even greater than the 
fourfold concentration which Biggar and associates state was required for normal 
phagocytosis. Increasing dilutions of homozygous CF sera with either Hanks balanced 
salt solution or normal human serum, thus decreasing its concentration, increased 
the capacity of the rabbit alveolar macrophages to phagocytize and kill 
Pseudomonas aeruginosa. Increasing concentrations had just the opposite effect. Suspension of 
rabbit alveolar macrophages in human serum reduced their phagocytic activity, but 
activity was reduced more by human CF serum than by human 
normal serum. This is not unexpected because high human serum concentrations 
are likely to be toxic to rabbit alveolar macrophages. Because the 
inhibition of phagocytosis was absent when homozygous CF serum more than 
24 hours old or previously heated or frozen was used and 
because of our observations that dilution increased macrophage phagocytic ability, we 
feel our data demonstrate the presence of a labile inhibitor rather 
than a deficiency. Since it is well known that CF patients 
have normal or elevated concentrations of immunoglobulins including IgA in their 
sera and pulmonary secretions and respond to infection, and IgA has 
not been shown to be essential for alveolar macrophage phagocytosis of 
Pseudomonas aeruginosa, we cannot agree that this inhibition is due to 
an IgA deficiency. We also note that some of the sera 
used in the experiments of Biggar and associates were stored at 
-70 degrees C. Perhaps this may account for the difference in 
results. 