Correlation of Alternative Pathway (AP) Lytic Activity and AP-Dependent Neutrophil Phagocytosis with Factor B Levels and Consumption in Serum

Abstract

This work investigated the correlation between serum levels of factor B, AP-lytic activity, ratio of factor B activation by zymosan, and AP-dependent neutrophil phagocytosis in samples of normal human serum (NHS). In addition, since the antithyroid drug propylthiouracil (PTU) induces increased levels of AP lytic activity in rats, groups of these animals were treated with this drug in order to increase AP titers and to evaluate those parameters also in this condition. The results showed no correlation between factor B concentration and AP lytic activity in 18 samples of NHS or between factor B concentration and proportion of consumption by zymosan. Interestingly, this consumption was also not correlated with phagocytosis as measured by the chemiluminescence (CL) response of neutrophils to the opsonized particles. The two biological properties of phagocytosis and lytic activity, dependent of AP, were not correlated to each other in the NHS samples. In the samples of rat serum with increased AP lytic levels a different result was observed. A positive correlation between CL response and lytic activity occurred in serum of animals receiving a low PTU dose, but not in serum of animals receiving a high dose, where CL responses were lower than those of controls.

The results are compared to literature data and discussed in terms of individual differences in resistance or susceptibility to infections and or diseases involving the complement system.

Key Words:

• AP-lytic activity
• AP dependent phagocytosis
• factor B x AP activity