Trypsin does not reconstitute responsiveness to lipopolysaccharide in the strain C3H/HeJ, but is a B-cell mitogen-like lipopolysaccharide, stimulating a different subpopulation

Characterization of a trypsin-like serine protease of activated B cells mediating the cleavage of surface proteins

Activated B cells may cleave their surface receptors due to the proteolytic activity on the cell membrane or in its vicinity. We attempted to isolate and characterize the protease(s) responsible for this cleavage. Zymograms prepared from the supernatant and the plasma membrane fraction of activated human B cells and BL41/95 cell line exhibited a 85-90 kDa doublet band with protease activity, while that of resting B cells did not. Soybean trypsin inhibitor (STI), Nalpha-p-tosyl-L-lysine chloromethyl ketone (TLCK) and EDTA treatment abolished the activity of this protease. The excess of Zn(2+) ions in EDTA did not restore the enzymatic activity, while it was completely recovered in the presence of Ca(2+). We affinity-purified a 85-90 kDa protease from the supernatant of BL41/95 cells using STI coupled to Sepharose 4B beads, and measured its kinetic parameters. For the arginyl substrate K(M) was 358+/-59 microM and for the lysyl substrate 582+/-103 microM. TLCK and benzamidine inhibited the protease at micromolar, while STI at nanomolar concentrations. Both the inhibition profile and the substrate specificity suggest that it is a trypsin-like serine protease. We assume that the 85-90 kDa serine protease expressed on and secreted by activated B cells and BL41/95 cell line is responsible for the cleavage of various membrane proteins, including Fcgamma receptors; thus it may play a crucial role in regulating B cell's function.

Optimal conditions for blastogenic response of peripheral blood lymphocytes to T and B cell mitogens in cynomolgus monkeys

Optimal conditions for the mitogen-induced proliferation of T and B lymphocytes of cynomolgus monkeys were determined. The T cell mitogens concanavalin A and phytohemagglutinin, at concentrations of 1.25-10 μg/ml and 1.25-10 μg/ml, respectively, and the T and B cell mitogen pokeweed mitogen, at concentrations of 0.2-10 μg/ml, induced high lymphoproliferative responses, the average stimulation index (SI) being 34-93. Since suitable mitogens have not been reported for monkey B cells, we tested three types of lipopolysaccharide (LPS): two derived from Escherichia coli-one extracted with phenol and one extracted with trichloroacetic acid (TCA); and one derived from Salmonella typhimurium, extracted with phenol. All three LPS had a high mitogenic effect for monkey lymphocytes, with SI of 2.3-6.4. The highest response was observed for 25 μg/ml of Salmonella LPS, and the addition of trypsin to the culture augmented the proliferative response of low or non-responder lymphocytes. © 1994 Wiley-Liss, Inc.

A trypsin-like serine protease activity on activated human B cells and various B cell lines

We have studied the trypsin-like serine protease activity of human tonsillar B lymphocytes. The lysate of the low-density, in vivo activated B cells as well as the lysate of cells stimulated with anti-human IgM F(ab')2 show elevated trypsin-like serine protease activity compared to the resting subset as monitored by the cleavage of Tos-Gly-Pro-Arg-pNA. The cleavage is sensitive to N-tosyl-L-lysyl-chloromethyl ketone and benzamidine but not to iodoacetamide. Experiments with intact cells give similar results. The finding that the intact cells hydrolyze the substrate, while their supernatant does not, suggests that the protease activity is cell membrane associated. It is possible that C3 is a substrate of the enzyme since the activated B cells cleave C3, whereas the resting B cells do not, and also C3 inhibits the enzyme-substrate reaction. In addition to the ex vivo B cells, we studied the serine protease activity of certain well-characterized B cell lines. The results show a correlation between the phenotype and the enzyme expression of the cell lines. BL41, an Epstein-Barr virus (EBV)-negative Burkitt lymphoma line, with a resting phenotype, has low activity, while its EBV genome-carrying convertants E95-A-BL41, E95-C-BL41, EHR-A-BL41 and BL41/95 that have the phenotype of activated B cells, have high proteolytic activity. The lymphoblastoid cell line WW-1-LCL which has the phenotype of an immunoblast, has the highest serine protease activity. On the basis of the above data, we suggest that a rather tight correlation exists between the degree of activation and the appearance of serine protease(s) on the surface of human B cells.