Plasma Ig level was determined according to the method described
by Siwicki and Anderson (1993). The oxidative radical production by
phagocytes during respiratory burst was measured using the NBT
(nitro-blue-tetrazolium) assay described by Anderson and Siwicki
(1995). A turbidimetric assay was used to determine serum lysozyme
levels using the method described by Hultmark et al. (1980) with
slight modifications. Serum MPO activity was measured according
to Quade and Roth (1997). SOD activity was measured by the percentage
reaction inhibition rate of enzyme with WST-1 (water soluble
tetrazolium dye) substrate and xanthine oxidase using a SOD
Assay Kit (Sigma, 19160) according to the manufacturer's instructions.
Serum antiprotease activity was measured according to the method
described by Ellis et al. (1990) with slight modifications (Magnadóttir
et al., 1999).