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In order to directly monitor neutrophil aggregation, we have developed a simple particle counting technique using flow cytometry. Flow times were used to determine aggregation from changes in the total number of particles per unit volume (%PA(T)), while fluorescent signals emitted from glutaraldehyde-fixed neutrophils were used to measure changes in the total number of singlet neutrophils (%PA(S)). Flow cytometrically-determined %PA values were found to be virtually identical to values determined from microscopy. We show that aggregation parameters can be evaluated and compared simply from measures of changes in total particle count without a need for distinguishing singlets from multiplets. A number of aggregation parameters are introduced and related to the initial cell concentration (N(o)) and stir speed (shear). Aggregation of neutrophils, following stimulation with 0.5 microM FMLP (N-formyl-methionyl-leucyl-phenylalanine), showed a latent time (tl) of 4 +/- 1.5 sec independent of N(o) or stir speed; had a forward rate of aggregation (vf) which was proportional to the initial cell concentration and the stir speed; plateaued for greater than or equal to 60 s; and showed partial to complete reversal by 7.5 min. Above a critical stir speed, the extent and duration of aggregation varied inversely with the stir speed. The stir and N(o) dependence of the aggregation parameters studied suggest the existence of subpopulations of neutrophils with distinct efficiencies of aggregation.

A gram-positive, anaerobic, chain-forming, rod-shaped anaerobe (isolate G20-7) was isolated from normal human feces. This organism was identified by cellular morphology as well as fermentative and biochemical data as Eubacterium aerofaciens. When isolate G20-7 was grown in the presence of Bacteroides fragilis or Escherichia coli (or another 7 alpha-hydroxysteroid dehydrogenase producer) and chenodeoxycholic acid, ursodeoxycholic acid produced. Time course curves revealed that 3 alpha-hydroxy-7-keto-5 beta-cholanoic acid produced by B. fragilis or E. coli or introduced into the medium as a pure substance was reduced by G20-7 specifically to ursodeoxycholic acid. The addition of glycine- and taurine-conjugated primary bile acids (chenodeoxycholic and cholic acids) and other bile acids to binary cultures of B. fragilis and G20-7 revealed that (i) both conjugates were hydrolyzed to give free bile acids, (ii) ursocholic acid (3 alpha, 7 beta, 12 alpha-trihydroxy-5 beta-cholanoic acid) was produced when conjugated (or free) cholic acid was the substrate, and (iii) the epimerization reaction was at least partially reversible. Corroborating these observations, an NADP-dependent 7 beta-hydroxysteroid dehydrogenase (reacting specifically with 7 beta-OH-groups) was demonstrated in cell-free preparations of isolate G20-7; production of the enzyme was optimal at between 12 and 18 h of growth. This enzyme, when measured in the oxidative direction, was active with ursodeoxycholic acid, ursocholic acid, and the taurine conjugate of ursodeoxycholic acid (but not with chenodeoxycholic, deoxycholic, or cholic acids) and displayed an optimal pH range of 9.8 to 10.2