SUMMARYHelicobacter pylori-induced in vitro stimulation of mononuclear cells was characterized by measuring DNA synthesis response, interferon-gamma (IFN-y) secretion and the number of immunoglobulinsecreting cells. The strength of these responses was measured in 51 subjects comprising 36 dyspeptic patients from the Gastroenterological Unit and 15 members ofthe laboratory staff. Nineteen subjects had antibodies to H. pylori and 32 did not. The responses were compared with respect to H. pylori antibody status. Positive stimulation of DNA synthesis (stimulation index > 2) was obtained in 96% of the subjects, and the bacterium induced IFN-y secretion in all of them. The induction of immunoglobulin-secreting cells revealed B cell in vitro stimulation. The antibody-positive subjects had a tendency to synthesize less DNA (Pnol significant) and secrete less I FN-y (F < 0-05) in response to H. pylori than did the antibody-negative ones, but the differences were not marked. The results show that the whole H. pylori bacterium stimulates mononuclear cells. The nature ofthe stimulation is not yet characterized (non-specific versus specific).

The T-cell response induced by Francisella tularensis antigen in sensitized subjects was characterized in vitro by measuring DNA synthesis in whole-blood and mononuclear cell cultures, interleukin 2 (IL-2) and gamma interferon (IFN-gamma) production, and IL-2 receptor expression. Correlations between these variables were estimated. The strengths of the responses were compared in 21 subjects naturally infected 2 years ago, 6 subjects vaccinated 5 to 6 years ago, and 13 control subjects with no history of infection or vaccination. Subjects with a history of natural infection synthesized more DNA in both whole-blood and mononuclear cell cultures, secreted more IL-2 and IFN-gamma, and expressed more IL-2 receptors than control subjects did. All these responses differed highly significantly (P less than 0.001) from those of the control subjects. The vaccinees exhibited somewhat lower responses than the naturally immunized subjects did, but the vaccinees could be distinguished from the control subjects by their DNA synthesis, receptor expression, and IFN-gamma production (P less than 0.01 to 0.001). The vaccinees showed a lower response, in terms of DNA synthesis and IL-2 secretion (P less than 0.05), than the infected group did but responded in a manner similar to that of this group, with respect to receptor positivity and IFN-gamma secretion (P greater than 0.10). The correlations between all the T-cell functions were good, with highly significant correlations (P less than 0.001) between whole-blood DNA synthesis and IL-2 and IFN-gamma secretion and between the two lymphokines (P less than 0.001). The results not only increase our knowledge of the T-cell response to tularemia antigen but also give an alternative approach to DNA synthesis measurement for the quantitation of T-cell responses. The results for the low-responding sensitized subjects seem to indicate that the parameters were comparable in sensitivity.

Plasma membrane was isolated from Streptococcus cremoris using mutanolysin from a streptomycete as the cell wall‐degrading enzyme and phenylmethylsulfonyl fluoride as protease inhibitor. The specific activity of membrane‐bound enzyme, adenosine triphosphatase (ATPase), was 4 μmol/mg protein per min, which was 5–10 times higher than the activity found in other fractions obtained during the isolation procedure. The number of polypeptides in the plasma membrane was approximately 50 with molecular weights 13 500–100 000, minor changes in the polypeptide pattern were observed when the plasma membrane was isolated without a protease inhibitor. The chemical composition of the membrane preparation was 49.7% protein, 21.9% lipid, 5.1% aminosugars, 17.3% RNA and 0.03% DNA. Electron microscopic examination confirmed the membrane to be practically devoid of cell wall components. Our results indicate that the membrane integrity is well retained and therefore the membrane preparation is suitable for detailed studies on vectorial metabolism and its enzymes, e.g. ATPase.

The presence of lipoteichoic acid (LTA) in plasma membrane and released adenosine triphosphatase (ATPase) preparations of Streptococcus lactis subsp. cremoris HA was studied by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS‐PAGE). The membrane preparation gave two spots with periodic acid Schiff's (PAS) staining. The reference LTA revealed one CBB stainable band with MW 21 500, and was detected as a characteristic yellow spot in the molecular weight area 14 000–20 900 with silver staining and was also stainable with PAS. A slight colour was found with PAS in the F1‐ATPase (EC 3.6.1.3) preparation. The results suggest that the carbohydrate component in the membrane preparation and in the solubilized F1‐ATPase is LTA.