Calculation of secretory antibodies and immunoglobulins

There is increasing evidence for the secretion of IgG and IgE, as well as IgA, antibodies by the nasal mucosa. Because the former immunoglobulins lack an identifiable secretory piece, estimates of their secretion have been based on their ratio to albumin or to total immunoglobulin of the same type in the nasal secretion as compared with serum. It is shown, however, that use of the ratio to albumin will result in large errors if the amount of antibody secreted by the nose is relatively small, and ratios based on total secretory Ig will, at least hypothetically, lead to error if antibodies with multiple specificities are being secreted. It is suggested that a more valid quantitation will be obtained from the expression

$INS=\frac{{Ab}_N}{{Alb}_N}-\frac{{Al}_S}{{Alb}_S}$

where INS is an index of nasal secretion, Ab = antibody, Alb = albumin, N = nasal secretion, and S = serum.