The presence and measurement of secretory component in human bile and blood

Comparison of secretory component for immunoglobulin A with albumin as reference proteins in tracheal aspirate from preterm infants

OBJECTIVES

To determine whether the concentration of secretory component (SC) in tracheal aspirate samples is less altered by changes in alveolar-capillary permeability and thus is a more reliable reference standard than albumin for the measurement of other components obtained by saline lavage in preterm infants.

METHODS

A total of 1229 tracheal aspirate and 1530 blood samples were collected from 195 neonates to evaluate the effects of advancing postnatal and gestational age, resolution of acute respiratory distress syndrome (RDS), steroid therapy for chronic lung disease, and acute sepsis on tracheal aspirate SC and albumin levels. The tracheal aspirate and blood samples were analyzed by enzyme-linked immunosorbent assay techniques for SC and albumin concentrations.

RESULTS

The mean values for the concentrations of aspirate and plasma SC did not vary significantly during an 8-week study period (n = 100) and did not vary with either gestational age (23 to 36 weeks) or postnatal age. Albumin concentration significantly decreased in aspirate samples from 1.67 +/- 0.77 mg/dl at week 1 to 0.41 +/- 0.21 mg/dl at week 8 (p < 0.001), whereas serum levels increased from 2.65 +/- 0.36 to 2.99 +/- 0.54 gm/dl (p < 0.001), suggesting a decrease in alveolar-capillary leakage with advancing postnatal age. The concentration of SC in aspirate samples from 51 infants who received dexamethasone remained constant during the first week of therapy, whereas the concentration of albumin decreased from 1.33 +/- 0.91 mg/dl at the initiation of therapy to 0.51 +/- 0.34 mg/dl on treatment day 7 (p < 0.001). The onset of sepsis (n = 40) was not accompanied by a significant change in either aspirate SC or albumin levels. However, in infants who had a deterioration in respiratory status concomitant with the onset of sepsis (n = 10), the levels of aspirate albumin increased whereas serum levels decreased (p < 0.001), suggesting an increase in alveolar-capillary leakage; the levels of aspirate SC remained unaltered.

CONCLUSIONS

Secretory component may serve as a more valid reference protein for the standardization of tracheal aspirate collection in preterm infants during evaluation of changes in inflammatory mediators in disease states and therapeutic interventions that alter alveolar-capillary integrity.

Serum secretory IgA and secretory component in patients with non-cirrhotic alcoholic liver diseases

Elevated levels of secretory IgA in serum have been demonstrated in several liver dysfunctions such as hepatic cytolysis and cholestasis. However, these possible alterations at an early stage of liver diseases have not yet been investigated. We studied a cohort of chronic alcoholic patients without cirrhosis in order to assess the changes in serum secretory IgA and other forms of secretory component, the split product of the polymeric Ig-receptor of epithelial cells. The possible diagnostic value of these measurements in the assessment of alcoholic disease was compared to that of serum gamma-glutamyl transpeptidase activity. Serum levels of secretory IgA and IgM and free secretory component, were quantified by an enzyme-linked immunosorbent assay in 71 patients with chronic alcoholic liver disease without cirrhosis and in 45 healthy controls. Patients were divided into two groups according to the severity of the liver abnormalities. In addition, the reversibility of serum secretory IgA, IgM and free secretory component abnormalities after alcohol withdrawal was evaluated in 15 patients. Serum levels of the three molecular forms of secretory component were significantly higher than those measured in control subjects, both in the whole population of patients and in the two groups of alcoholic patients without cirrhosis. In all groups, serum secretory IgA levels were correlated to free secretory component but not to total IgA levels. Serum secretory IgA levels were as discriminative as gammaglutamyl transferase activity in distinguishing between chronic alcoholic patients without cirrhosis and non-alcoholic subjects. The abnormalities of serum secretory IgA concentrations were reversible after alcohol withdrawal.(ABSTRACT TRUNCATED AT 250 WORDS)

Secretory immunoglobulins in serum from human immunodeficiency virus (HIV)-infected patients

Infection by the human immunodeficiency virus is associated with polyclonal B cell activation and increased levels of serum IgA. In order to characterize the molecular species of serum IgA, we have measured total IgA, IgA1, and IgA2 in sera from 60 HIV-1-infected patients and 40 healthy controls. In addition, secretory IgA (S-IgA), secretory IgM (S-IgM), free immunoreactive secretory component (SC), and the distribution of monomeric and polymeric IgA were determined. The data confirm the elevation of total serum IgA levels in HIV-1-infected patients, and both IgA1 and IgA2 concentrations are elevated. Furthermore, the data show a substantial increase in serum levels of both monomeric and polymeric IgA. Serum S-IgA levels were significantly increased in CDC group II patients versus controls and more frequently elevated in CDC group IV patients. The highest S-IgA levels were found among patients with the lowest blood CD4+ cell counts. Serum S-IgA levels were not correlated with serum levels of either total IgA or polymeric IgA. Serum S-IgM levels were also increased in HIV-1-infected patients and positively correlated with serum S-IgA levels. Conversely, serum levels of free SC were not altered. An increase in serum S-IgA was not related to human hepatitis B virus infection and/or to hepatic dysfunction or to diarrhea or overt intestinal infection. The data indicate that secretory Ig (S-IgM and S-IgA), which are likely to be produced at mucosal sites, increase in the serum of HIV-1-infected patients.

Polymeric Ig receptor expression in hepatocellular carcinoma

The cellular localisation of the polymeric Ig receptor (pIg-R) and carcinoembryonic antigen (CEA), hepatic and biliary cell markers, were investigated in patients with hepatocellular carcinoma (HCC) and high serum levels of secretory component. Serum SC were increased 6-20-fold in 8 HCC patients compared with normal subjects. Serum free SC was positively correlated bilirubin (r = 0.95, P less than 0.04). In normal liver tissue, cytokeratin (CK) 8 and 18 were localised in hepatocytes and biliary cells while pIg-R and CK 19 expression was restricted to biliary cells. In tumoral liver tissue, malignant cells expressed CK 8 and 18 weakly; pIg-R and CK 19 were not detected in tumoral cells. CEA was expressed by biliary cells in normal and proliferating ducts. In peritumoral fibrosis, proliferating biliary cells were strongly stained by anti-cytokeratins and anti-pIg-R antibodies. In one case, pIg-R was localised in isolated cells close to fibrosis without co-staining of anti-CK 19. Thus increased serum SC is not associated with pIg-R expression by tumoral cells, and pIg-R may be considered an additional marker of biliary cells. High SC might be explained either by reflux from bile to serum and/or release of unbound SC from the vascular pole of non-functional, proliferating biliary structures.