Analysis of immunoglobulins in sarcoidosis

Assessment of local immunoglobulin(Ig)-production in sarcoidosis may be indicative of disease activity. However, in interstitial lung disease an increase in protein leakage across the alveolar-capillary membrane complicates determination of local Ig-production. In order to overcome this problem, techniques successfully used for the evaluation of local Ig-production in cerebrospinal fluid were applied to bronchoalveolar lavage (BAL)-analysis.

Ten patients with biopsy-proven sarcoidosis, seven patients with respiratory infections and ten patients as controls without any sign of interstitial lung disease or infection underwent BAL. Equal amounts of total protein (2 micrograms/lane) from BAL and serum samples were run on SDS-PAGE gradient-gel and blotted to a nitro-cellulose membrane. The blots were stained for total protein, IgA, IgM, IgG and IgG1-4-subgroups.

Densitometric analysis revealed a significant increase of the IgG/albumin-ratio in BAL of sarcoidosis patients compared to the control group. In all control patients a single IgG band of identical molecular weight was detected both in serum and BAL. In sarcoidosis and pneumonia the serum showed multiple bands distinct from the BAL-band in regard to molecular weight. Subclass analysis of this group revealed an increased band intensity and different molecular weight of IgG1, IgG2 and IgG4-bands in BAL compared to serum indicative of local production. IgA and IgM were detected in all samples without any significant differences between the three groups.

Molecular weight analysis of IgG-subgroups revealed local production of IgG1,2+4 in sarcoidosis and respiratory infection. This technique may prove useful with regard to the assessment of disease activity in sarcoidosis.