Measurement of IgG, IgM and IgA concentrations in canine serum, saliva, tears and bile.

Capture ELISAs, for canine IgG, IgM, IgA and albumin, were developed and used to analyse immunoglobulin (Ig) concentrations in both serum and secretions. Matched samples of serum, saliva and tears were taken from 31 dogs, assigned to two groups based on age, whilst bile samples were obtained from nine adult dogs at post-mortem. Serum and tear IgA concentrations were significantly lower in dogs < or = 12 months of age compared with dogs > 12 months of age (p = 0.006 and 0.045, respectively). There was no significant correlation between serum and secretory Ig levels, with the single exception of serum and tear IgM concentrations (rp = 0.553, p = 0.004). IgG and IgM concentrations were significantly correlated in matched tear and saliva samples (IgG: rp = 0.470, p = 0.023; IgM: rp = 0.651, p < 0.0001). Albumin concentrations were significantly correlated with IgG, but not IgM or IgA, in both saliva and tears (saliva, rp = 0.581, p = 0.004; tears, rp = 0.843, p < 0.0001) whilst IgA and IgM concentrations were significantly correlated with each other in both secretions (saliva, rp = 0.644, p = 0.001; tears, rp = 0.555, p = 0.009). Significantly, more Ig of all classes was secreted into saliva than tears as calculated by a secretory index. A large diurnal and day-to-day variation was observed in Ig concentrations in serial saliva and tear samples taken from a further four dogs. Serum Ig concentrations are therefore, poor indicators of mucosal secretion in this species and significant intra-individual variation exists in secretory Ig levels. Both findings should be taken into account in future studies of canine mucosal immunoglobulins.