IGG SUBCLASSES IN THE LUNGS OF PATIENTS WITH INTERSTITIAL PNEUMONITISFOLLOWING BONE-MARROW TRANSPLANTATION

Subclasses of immunoglobulin G (IgG) were measured in bronchoalveolar lavage (BAL) fluid and serum from rive normal volunteers and 25 bone m arrow transplant (BMT) recipients, who developed 32 episodes of pneumo nitis. Evidence for local production of the four subclasses was sought , to assess whether any observed deficiency was associated with any pa rticular group of pulmonary infections. In the normal volunteers, IgG1 and IgG4 could be detected in BAL fluid from all subjects, with evide nce for local production of IgG1 in one, and IgG4 in all five. IgG2 co uld be detected in BAL fluid from one subject, but IgG3 was undetectab le in all normal BAL fluid. The BMT recipients differed from the norma l volunteers mainly in the presence of IgG2 and IgG3 in BAL fluid. Fur thermore, IgG4 could not be detected in BAL from seven. Furthermore, I gG4 could not be detected in BAL from seven episodes of pneumonitis (s ix patients). Bacteria, protozoa or fungi alone were isolated from fiv e of these seven lavages, whereas pneumonitis associated with these or ganisms alone only occurred in 9 of the remaining 25 episodes of pneum onitis (19 patients) where there was also evidence for local productio n of IgG4. Moreover, 4 out of 7 patients with no detectable IgG4 in la vage developed secondary infections, whilst only 5 out of 19 patients producing IgG4 locally developed secondary infections (p=0.05). Althou gh there was individual variation within each group, levels of local p roduction of both IgG1 and IgG4 tended, however, to be higher in patie nts who died from pneumonitis than in those who recovered, suggesting that this may be a poor prognostic maker. These results suggest that I gG4 is an important immunoglobulin subclass in the lower respiratory t ract, and may have a protective role against bacterial and fungal infe ctions. Excessive local production of IgG1 and IgG4, however, could be associated with a poor prognosis.