Effect of polypeptide hormones on stimulation of casein secretion by mouse mammary epithelial cells grown on floating collagen gels.

The in vitro effects of protein hormones on the stimulation of casein secretion by mouse mammary epithelial cells were studied. Mouse mammary glands were enzymatically dissociated and used immediately or were stored frozen and thawed just before use. Cells were cultured on floating collagen gels in the presence of insulin, cortisol and a pituitary or placental polypeptide hormone. Casein, released into the medium, was assayed by a radioimmunoassay against one of the components of mouse casein. Mammary cells released casein into the medium in the presence of as little as 10 ng of ovine prolactin per ml of medium. Human growth hormone stimulated the casein secretion to the same extent as prolactin. Human placental lactogen, ovine and bovine growth hormones were less stimulatory. Luteinizing hormone, follicle-stimulating hormone and thyroid-stimulating hormone had no effect on the stimulation of casein secretion.

Neuraminidase activity and free sialic acid levels in the serum of patients with acute poststreptococcal glomerulonephritis.

It has been suggested that in acute poststreptococcal glomerulonephritis, streptococcal neuraminidase may remove sialic acid from some normal plasma or tissue components, thus rendering it antigenic. We therefore investigated serum neuraminidase activity and serum and urinary free neuraminic acid levels, using the thiobarbituric acid method, in 39 patients with acute poststreptococcal nephritis. Serum neuraminidase activity was found in eight patients, and increased thiobarbituric acid-reactive material (presumed to be free neuraminic acid on the basis of absorption-spectrum similarity) was found in 28 patients. Serial determinations in 21 patients indicated that neuraminidase activity was present only initially and that free neuraminic acid levels decreased with time, usually becoming undetectable after four weeks. Determinations in patients with other renal and nonrenal diseases suggested that the findings were characteristic of poststreptococcal nephritis. Urinary neuraminic acid levels were unrelated to serum levels and were not markedly different between patients and normal subjects. These data suggest a role for neuraminidase activity in acute poststreptococcal nephritis, but they do not indicate whether it is primary or secondary.

Neuraminidase production by streptococci from patients with glomerulonephritis.

Autoantigenic events in acute poststreptococcal glomerulonephritis (APSGN) may result from neuraminidase-induced alterations in immunoglobulin levels. Whether streptococci from patients with APSGN produced neuraminidase and, if so, what substrates could be used for screening purposes and what were of potential clinical relevance were determined. Group A streptococci cultured from 20 patients with APSGN and four patients with acute rheumatic fever and group B, C, D, and G streptococci cultured from other individuals were reacted with the substrates to determine neuraminidase activity by the thiobarbituric acid assay. Neuraminidase production was detected in 16 of 20 streptococci from patients with APSGN. Partial purification by Sephadex G-150 chromatography gave two peaks, and polyacrylamide gel electrophoresis gave two bands with neuraminidase activity. Bovine mucin was the most useful substrate to detect neuraminidase production by nephritogenic streptococci, and with respect to human substrates, IgM was the most sensitive and renal basement membrane the least sensitive to enzyme action.

Isolation of parietal cells from guinea-pig gastric mucosa and the immunological characterization of their antigenic structure.

A method is described for the isolation of parietal cells from the gastric mucosa of the guinea pig by enzymatic digestion with collagenase. A suspension was obtained that contained 70-80% parietal cells. About 80% of the cells were viable immediately after incubation, but viability dropped sharply after one hour. Parietal cells were identified by their morphology on light and electron microscopy, by their uptake of neutral red, by immunofluorescent staining and by carbonic anhydrase activity. Antibodies to four distinct parietal-cell antigens were obtained from rabbits immunized with the isolated parietal cells or fractions thereof. These antibodies were directed against the microsomal fraction of the parietal-cell cytoplasm, the plasma and nuclear membranes, the soluble proteins, and Castle's intrinsic factor. The antibody against the microsomal fraction, though reacting in the same way as the antibody to parietal cell canaliculi found in the serum of patients with pernicious anaemia, showed greater species specificity.