Surfactant Protein D Family: Potential for Diagnosis or Monitoring Therapy in Autoimmune Diseases?

In this issue of The Journal , Soto-Cardenas, et al examine the frequency of a genetic polymorphism that is associated with elevated surfactant protein D (SP-D) levels and assess levels in a cohort of 210 consecutive patients with primary Sjogren syndrome (pSS)1. They find elevated SP-D levels in patients with severe glandular involvement, hypergammaglobulinemia, leukopenia, and extraglandular manifestations including pulmonary and renal. A key observation of the Soto-Cardenas, et al report is that elevation of SP-D was found in a subset of pSS patients with interstitial pulmonary involvement (1054 vs 700 ng/ml, p = 0.029). This raises the possibility that SP-D may be a marker for early pneumonitis or its progression, as has been suggested in both scleroderma lung disease2,3 and nonspecific interstitial pneumonitis (NSIP)4. They also found significant elevation in a subset with renal disease (1880 vs 716 ng/ml, p = 0.002). This finding is potentially of interest, because SP-D elevation has not previously been reported, according to a Medline search, in patients with interstitial nephritis. Their report presents 3 basic observations. First, patients with pSS exhibit a polymorphism of the gene encoding the SP-D at roughly the same frequency as found in healthy controls. Thus, elevation of SP-D in their patients with pSS could not be attributed simply to genetic polymorphism. An elevated frequency of the T/T genotype was found in patients … Address correspondence to Dr. R.I. Fox, Rheumatology Clinic, Medicine, 9850 Genesee, #910, La Jolla, California 92037, USA. E-mail: robertfoxmd{at}mac.com