Characterization of molecular components associated with surface immunoglobulin M in human B lymphocytes: presence of tyrosine and serine/threonine protein kinases

To characterize the signal transduction through the antigen receptor (AgR) on human B lymphocytes, we analyzed its association with other molecular components. The surface IgM (sIgM) complex isolated in digitonin contains two surface expressed polypeptides--the previously described Ig alpha and Ig beta proteins--covalently linked to each other in a 48/39-kDa heterodimer. We show herein that the human sIgM complex isolated from the Burkitt's lymphoma cell line, Ramos, or from dense tonsillar B cells contains additional molecules--160 kDa and 75 kDa in size--and enzymatic activities able to phosphorylate on tyrosine as well as serine/threonine residues the 39-, 48-, 75- and 160-kDa polypeptides. By specific immunoprecipitation with antibodies to src-family kinases, we consistently detected p56lyn in the sIgM complex. In the Ramos cell line, both p56lck and p59fyn activity were also observed, although to a much lesser extent than p56lyn. These kinases are associated with sIgM before cell stimulation. As shown by two-dimensional electrophoresis, they interact in a tight complex with multimeric forms of the Ig alpha and Ig beta components. The kinases are active in vitro but must be highly regulated in vivo: Western blotting with anti-phosphotyrosine antibodies revealed that stimulation of the AgR on viable B cells increased detectable phosphotyrosine residues on the components present in the sIgM complex. Based on these phosphorylation changes, the 39-, 48-, 75- and 160-kDa molecules are likely to be functionally active elements in an IgM complex crucial for the transduction of the antigenic signal.

Immunoregulatory functions of paf-acether. VI. Dual effect on human B cell proliferation

The role of paf-acether (paf), a phospholipid cytokine, in the modulation of human B cell function was investigated. Paf, from 1 x 10(-5) M to 10(-6) M, decreased B cell proliferation induced by both phorbol myristate acetate (PMA) and anti-IgM antibodies (anti-IgM Ab). By contrast, 1 x 10(-7) M to 1 x 10(-9) M paf enhanced PMA triggered, but not anti-IgM triggered B cell proliferation. B cell proliferation was modulated between 24 and 72 hr of culture indicating that the effect of paf did not merely reflect a shift in proliferation kinetics. Interestingly, paf also enhanced the spontaneous proliferation of a Burkitt lymphoma-derived B cell line, Raji, which suggests that paf can directly act on B cells. The modulatory effect of paf on peripheral blood B cells was independent of PMA concentration, yet the effect on Raji cells was dependent upon cell density. The data suggest that paf is a potent modulator of B cell function, and may be involved in the control of humoral immune response.

Thymic B cells from myasthenia gravis patients are activated B cells. Phenotypic and functional analysis

Thymic cell populations from 12 patients displaying myasthenia gravis were submitted to a phenotypic and functional study. Immunofluorescence analysis of thymic sections revealed the presence in germinal centers of B lymphocytes expressing the B cell markers--CD19, CD21, IgD, or IgM. After T cell and macrophage depletion of thymic single cell suspensions, B cell-enriched populations were isolated. Enriched B cells expressed at variable levels activation markers such as CD71, 4F2, CD23, and B8.7, indicating that a marked proportion of them are activated. Moreover, addition of B cell growth factor 12kDa and to a lesser extent of rIL-2 induced a spontaneous proliferation of these B cell populations. These functional and phenotypic signs of activation may reveal the first steps of an autoimmune response against acetylcholine receptor as enriched B cell populations have the capacity to spontaneously secrete anti-acetylcholine receptor antibody.

Thymic B cells from myasthenia gravis patients are activated B cells. Phenotypic and functional analysis

Thymic cell populations from 12 patients displaying myasthenia gravis were submitted to a phenotypic and functional study. Immunofluorescence analysis of thymic sections revealed the presence in germinal centers of B lymphocytes expressing the B cell markers--CD19, CD21, IgD, or IgM. After T cell and macrophage depletion of thymic single cell suspensions, B cell-enriched populations were isolated. Enriched B cells expressed at variable levels activation markers such as CD71, 4F2, CD23, and B8.7, indicating that a marked proportion of them are activated. Moreover, addition of B cell growth factor 12kDa and to a lesser extent of rIL-2 induced a spontaneous proliferation of these B cell populations. These functional and phenotypic signs of activation may reveal the first steps of an autoimmune response against acetylcholine receptor as enriched B cell populations have the capacity to spontaneously secrete anti-acetylcholine receptor antibody.

B8.7 antigen is present on B-cell precursor acute lymphocytic leukemia. Correlation with the low molecular weight B-cell growth factor responsiveness of these cells

The purpose of this study was to analyze the expression of B8.7 antigen and its implication in the low molecular weight B-Cell growth factor (LMW BCGF) proliferative pathway at the early stages of the human B-cell differentiation. After an overnight incubation in culture medium of B-cell precursor acute lymphoblastic leukemias (ALL), we demonstrated the presence of B8.7 antigen in 18 of 25 cases (72%). Such an incubation also induced a significant increase in the LMW BCGF responsiveness of ALL cells (P less than 0.03). In addition, we showed a significant correlation between B8.7 expression and the ability of pre-B ALL cells to respond to LMW BCGF. As previously described for normal B cells, the anti-B8.7 monoclonal antibody inhibited the LMW BCGF-dependent proliferation of pre-B ALL cells in a dose-dependent manner. These data indicate that B8.7 antigen is expressed and may be functionally related to the LMW BCGF pathway at the pre-B cell stages of differentiation. These results also suggest that human B-cell precursor ALL are not only phenotypically similar to their normal B lymphocyte counterparts, but are also sensitive to the same immunoregulatory cytokines that control normal cell growth.

B8.7 antigen expression on B-CLL cells and its relationship to the LMW-BCGF responsiveness

In this work, we studied the expression of B8.7 antigen on B lymphocytes from patients suffering from B type chronic lymphocytic leukemia (B-CLL) as well as on non Hodgkin lymphoma cells (NHL). B8.7 is an activation marker, which has been reported to be associated with the capacity of activated B cells to respond to LMW-BCGF. B lymphocytes of 11 out of 22 patients tested were B8.7 positive. With the exception of one case, LMW-BCGF is able to induce DNA synthesis by these cells in the absence of costimulation by anti-mu antibodies (anti-mu Ab). The LMW-BCGF dependent proliferation of these malignant cells is inhibited by the anti-B8.7 monoclonal antibody (anti-B8.7 MoAb), in the same line as that of normal B cells. These results obtained with monoclonal B cells confirm that the B8.7 molecule is involved in the signalling pathway of the LMW-BCGF.

Effects of some poorly digestible carbohydrates on bile acid bacterial transformations in the rat

The effects of ingestion of poorly digestible carbohydrates on bacterial transformations of cholic acid and beta-muricholic acid were studied in rats fed on increasing levels of lactose, lactulose, amylomaize or potato starches. Each level was given for 3 weeks and, at the end of each dietary treatment, bile acid faecal composition was analysed and a group of six rats was killed every 4 h during 24 h to determine the amounts of fermented carbohydrate and fermentation characteristics (caecal pH, volatile fatty acids (VFA) and lactic acid concentrations). Fermentation of carbohydrates decreased caecal pH and enhanced caecal VFA and lactic acid concentrations. Irrespective of the poorly digestible carbohydrate, the variation of bacterial transformation always occurred in the same way: the bacterial transformation of beta-muricholic acid into hyodeoxycholic acid was the first to disappear, while omega-muricholic acid formation increased; second, cholic acid transformation decreased and finally all bile acid transformations were strongly affected. There was a significant correlation between bile acid transfer and the minimal caecal pH in vivo. This effect of pH was similar in vitro. To determine whether the levels of bacteria which transformed bile acids were modified, rats fed on the highest amounts of poorly digestible carbohydrates were introduced into isolators and carbohydrate feeding was stopped. Caecal pH recovered its initial value but bile acid transformations remained changed, suggesting that the intestinal microflora were modified by ingestion of fermentable carbohydrates.

Expression of the B8.7 antigen on hairy cells and relation with the LMW-BCGF response

Hairy cells are classified as B cell tumors at a preplasma cell stage of differentiation and are believed to represent cells undergoing a switch process. These cells are stimulated in vitro to DNA synthesis and multiplication in the presence of the lymphokine LMW-BCGF. We have tested the level of expression on these cells of the newly described B8.7 activation marker which has been reported to be associated with the capacity of various B cells to respond to LMW-BCGF. The presence of this marker has been readily detected on the hairy cells of 10 of the 12 patients tested in this study; interestingly, for one of the negative cases, the tumor cells were unable to proliferate in response to LMW-BCGF. As on normal B cells, a marked inhibition of the LMW-BCGF dependent response could be achieved in the presence of a monoclonal anti-B8.7 antibody, sustaining the proposal that the B8.7 molecule is involved in the signaling pathway of this growth factor. IFN-alpha is highly efficient in the therapy of hairy cell leukemia (HCL), and we confirm in the present study that IFN-alpha also inhibits the LMW-BCGF dependent proliferation of hairy cells in vitro. In addition, we show that this inhibition is independent of a significant modulation of the B8.7 antigen, a molecule putatively associated with the LMW-BCGF receptor.

A B cell-restricted activation antigen (B8.7) functionally related to the low molecular weight B cell growth factor receptor

A novel monoclonal antibody (anti-B8.7) is reported which recognizes an epitope expressed either on in vitro activated B cells or on a fraction of fresh large B cells (putatively in vivo preactivated). B8.7 antigen is also present on two out of eight B cell lines tested and is characterized as a membrane component displaying an approximate molecular weight of 55,000 to 60,000. By contrast, B8.7 is absent from resting B cells, monocytes, resting or activated T cells, and from the eight non-B cell lines tested. After in vitro activation, B8.7 antigen appears later than the transferrin receptor and its expression increases until day 3. The anti-B8.7 monoclonal antibody induces a dose-related inhibition of the low molecular weight B cell growth factor-dependent proliferation of activated B cells, whereas it does not affect their response to interleukin 2. This strongly suggests that the B8.7 epitope is present on a molecule selectively involved in the interaction between B cells and a B cell growth factor.

A B cell-restricted activation antigen (B8.7) functionally related to the low molecular weight B cell growth factor receptor

A novel monoclonal antibody (anti-B8.7) is reported which recognizes an epitope expressed either on in vitro activated B cells or on a fraction of fresh large B cells (putatively in vivo preactivated). B8.7 antigen is also present on two out of eight B cell lines tested and is characterized as a membrane component displaying an approximate molecular weight of 55,000 to 60,000. By contrast, B8.7 is absent from resting B cells, monocytes, resting or activated T cells, and from the eight non-B cell lines tested. After in vitro activation, B8.7 antigen appears later than the transferrin receptor and its expression increases until day 3. The anti-B8.7 monoclonal antibody induces a dose-related inhibition of the low molecular weight B cell growth factor-dependent proliferation of activated B cells, whereas it does not affect their response to interleukin 2. This strongly suggests that the B8.7 epitope is present on a molecule selectively involved in the interaction between B cells and a B cell growth factor.

Reactivity of Leu-1+ tonsillar B cells to a high molecular weight B cell growth factor

This work was focused on the responsiveness of B cells from blood and tonsils to typical B cell growth factors (BCGF) in the absence of anti-mu antibody. This direct responsiveness was not observed with small dense B cells from either organ. Large tonsillar B cells but not large blood B cells did respond directly to a high m.w. BCGF (m.w. 50,000 BCGF), whereas large B cells from both organs responded directly to the low m.w. BCGF (m.w. 20,000 BCGF). The tonsillar B cells directly responsive to the m.w. 50,000 BCGF express the 4F2 marker and thus belong to a population of in vivo-preactivated B cells. Moreover, this direct responsiveness to the m.w. 50,000 BCGF is localized in Leu-1+ tonsillar B cells. The Leu-1+ and Leu-1- tonsillar B cell subsets do not differ in their responsiveness to the m.w. 50,000 BCGF upon costimulation with anti-mu antibody and to the m.w. 20,000 BCGF regardless of the presence of anti-mu antibody. Thus, the Leu-1+ subset present in tonsils shows a particular reactivity to a high m.w. BCGF.

Reactivity of Leu-1+ tonsillar B cells to a high molecular weight B cell growth factor

This work was focused on the responsiveness of B cells from blood and tonsils to typical B cell growth factors (BCGF) in the absence of anti-mu antibody. This direct responsiveness was not observed with small dense B cells from either organ. Large tonsillar B cells but not large blood B cells did respond directly to a high m.w. BCGF (m.w. 50,000 BCGF), whereas large B cells from both organs responded directly to the low m.w. BCGF (m.w. 20,000 BCGF). The tonsillar B cells directly responsive to the m.w. 50,000 BCGF express the 4F2 marker and thus belong to a population of in vivo-preactivated B cells. Moreover, this direct responsiveness to the m.w. 50,000 BCGF is localized in Leu-1+ tonsillar B cells. The Leu-1+ and Leu-1- tonsillar B cell subsets do not differ in their responsiveness to the m.w. 50,000 BCGF upon costimulation with anti-mu antibody and to the m.w. 20,000 BCGF regardless of the presence of anti-mu antibody. Thus, the Leu-1+ subset present in tonsils shows a particular reactivity to a high m.w. BCGF.

Functional heterogeneity of nonresting B cells in human blood

Among human peripheral blood B cells we localized the precursors of two interleukin-dependent B cell activation processes: the specific response to a particulate antigen, trinitrophenylated polyacrylamide beads (TNP-PAA) and the polyclonally induced response to pokeweed mitogen. In both cases the precursors belong to the OKB7+, sIgD-, mouse red blood cell- subpopulation. However, they differ when cell density, reflecting the stage of activation reached by B cells in peripheral blood, is considered. Only B cells of intermediate density respond to TNP-PAA, whereas the optimal response to pokeweed mitogen is obtained with the cells displaying the lower density. The lack of response of the more dense (resting) B cells to TNP-PAA suggests that the T dependency of this antigen is not based on linked recognition, and fits with our demonstration that this particulate antigen can trigger B cells in the presence of T cell factor. More importantly, our results show that nonresting B cells are functionally heterogeneous according to their degree of preactivation: the responsiveness to specific signals provided by a nonmitogenic hapten-carrier conjugate would be acquired before that to polyclonal activators.

Dietary fiber and cholesterol and bile acid metabolism in axenic (germfree) and holoxenic (conventional) rats. III. Effect of non-sterilized pectin

Axenic (germfree) and holoxenic (conventional) rats were given a pectin-containing diet (5%) or a pectin-free diet. The diet was not sterilized and the axenic state was maintained by the addition of antibiotics. Pectin modified little or not at all the quantity of bile acids in the small intestine, fecal bile acid excretion and fecal elimination of the sum of cholesterol and bile acids. It similarly decreased the concentration of liver cholesterol and the amount of bile acids in the cecum and large intestine of both germfree and conventional rats. Pectin decreased the absorption coefficient of dietary cholesterol and its plasma concentration and increased fecal cholesterol elimination in conventional rats but not in germfree animals. The data imply that some of the actions of pectin depend on the presence of the intestinal flora but the exact nature of this relationship is unclear.

Effect of wheat bran upon gastro-intestinal transit in germ-free and conventional rats

Germ-free and conventional rats were fed a semi-synthetic diet including 10% wheat bran for 1 month. They were compared to similar rats fed the same diet without bran. Transit of polyethylene glycol (PEG) 4000 was studied in giving the marker either in saline or in the diet. The presence of a bacterial flora was found to accelerate small intestine transit and total transit. The ingestion of solid food slowed gastric emptying but had little effect on small intestine transit. Wheat bran slowed gastric emptying of PEG in most of the experimental groups. It had no significant effect on small intestine transit except in germ-free rats having received the marker in solid food. It accelerated total transit in germ-free and conventional rats. The results suggest that bran mainly exerts its action in the hindgut. The role of microflora in this action of bran is discussed.

Effect of amylomaize starch on cholesterol and bile acid metabolisms in germfree (axenic) and conventional (holoxenic) rats

Germfree and conventional rats were given a semi-synthetic diet containing either normal cornstarch or an amylomaize starch. The experimental groups thus formed were compared to assess the effects of these two types of starch and to determine if digestive tract microflora was involved in these effects. The presence of amylomaize starch decreased body growth in germfree and conventional rats, increasing food intake in the former and decreasing it in the latter. In conventionals, amylomaize starch decreased the apparent digestibility of the ration only slightly, while in germfrees it diminished apparent digestibility considerably. The cecal weight of germfree animals was not modified by amylomaize starch but that of conventional rats was increased fourfold. In both types of rat, amylomaize starch largely decreased the plasma concentration of cholesterol, largely increased the total amount of bile acids in the small intestine but slightly modified the fecal elimination of cholesterol and bile acids. It augmented the cholesterol concentration in the liver of germfrees and decreased it in conventionals while, on the contrary, it diminished the total amount of bile acids in the hind gut in the former and augmented it in the latter. This starch did not change bile acid deconjugation in conventional rats but considerably decreased other bacterial transformations of cholesterol and bile acids. Digestive tract microflora was undoubtedly involved in the action of amylomaize starch on cecal weight, ration digestibility, food intake, hepatic cholesterol concentration, the amount of bile acid in the hind gut and obviously in the transformation of cholesterol and bile acids. It did not play a role in the other effects of this starch: the strong decrease in the concentration of plasma cholesterol was the direct effect of amylomaize starch on rat metabolism.

Dietary fiber and cholesterol and bile acid metabolisms in axenic (germfree) and holoxenic (conventional) rats. I. -- Effect of wheat bran

Axenic (GF) and holoxenic (CV) rats were given a semi-synthetic diet containing no fiber (0) or 10 p. 100 bran (B). The GFO, GFB, CVO and CVB groups were compared to assess the action of the flora and the bran. The bran diet did not change body growth, food intake or cecal water content. It caused only a slight decrease in the digestive utilization of the diet in the holoxenic rats and a decline in cecal weight in the axenic rats. The bran diet modified unabsorbed cholesterol transit in both types of rats, and slightly altered dietary cholesterol absorption which was a little lower in axenics than in holoxenics. In the former (GF), the bran-containing diet dit not change either the plasma or the hepatic cholesterol concentration. In the latter (CV), it increased plasma cholesterol which was lower in CVO rats than in the other three groups and decreased hepatic cholesterol which was thus lower in the CVB lot than in the others. The bran diet reduced fecal cholesterol elimination in axenic and holoxenic rats. This decrease was a little higher in the latter. The digestive tract microbial flora was thus implicated in the effect of bran on those characteristics of cholesterol metabolism. The bran did not change fecal bile acid composition in the axenics. In the holoxenics, it contributed to make this composition uniform because without bran, individual compositions varied. The microbial flora thus changed many aspects of bran action on cholesterol and bile acid metabolisms. But total cholesterol and bile acid elimination was only slightly affected by those two factors.

Dietary fiber and cholesterol and bile acid metabolisms in axenic (germfree) and holoxenic (conventional) rats. II. Effect of pectin

Axenic and holoxenic rats were fed with a semi-synthetic diet containing 5 p. 100 pectin as the only fiber. Although the microbial flora of the digestive tract converted most of the bile acids in holoxenic rats, it hardly changed the other characteristics of cholesterol and bile acid metabolisms, except intestinal bile salt pools which were much larger in the axenic rats. When the pectin-containing and pectin-free diets were compared, it appeared that the former diet increased cecal weight, especially in axenic rats, but slightly modified cholesterol and bile acid metabolisms. However, the values of some characteristics of those metabolisms varied individually in the holoxenic rat fed with the pectin-containing diet, while they were very homogeneous in the other groups. This heterogeneity might result from pectin-digestive tract microbial flora interactions which would vary among individuals.

Variations of bile salt pool size and secretion rate in rats according to the modes of sterilization and preparation of a semi-synthetic diet

A semi-synthetic diet was sterilized by irradiation and given to rats as pellets, powder or paste obtained by admixing an equal amount of water. The bile salt pool increased from the first to the third treatment. That effect disappeared when the starch was replaced by sucrose or when the diet was autoclaved instead of irradiated. The bile duct secretion of bile salts varied according to the bile salt pool. Hypotheses are proposed to explain the relationship between the form of the diet and bile salt pool size and secretion.

Bacterial formation of omega-muricholic acid in rats

In the feces of conventional rats, the amount of omega-muricholic and hyodeoxycholic acids vary according to the diet. To understand this phenomenon, we investigated the bacterial formation of these bile acids. The present paper reports the first isolation, from conventional rat feces, of a strain of Clostridium group III which transforms beta-muricholic acid, the main bile acid in germfree rats, into omega-muricholic acid.

Measurement of fecal bile acid excretion in gnotobiotic rats: comparison of gas-liquid chromatography and [4(-14C)] cholesterol isotopic equilibrium

Gas-liquid chromatography (G.L.C.) and the method of [4(-14C)] cholesterol isotopic equilibrium (C.I.E.) were used to determine the fecal bile acid excretion in gnotobiotic rats. The same samples were submitted to both methods. In these conditions, it was observed that the fecal bile acid excretions determined by G.L.C. were 38% of lower than when determined by C.I.E. In thin-layer chromatographic analyses (T.L.C.) of the bile acid extracts obtained from rats in which a [4(-14C)] cholesterol isotopic equilibrium was established, 33 to 35% of the radioactivity of this fraction was not observed in the rat primary bile acids. No bile acids could be observed in G.L.C. made with eluates obtained from the T.L.C. areas containing this radioactivity. It therefore appears that the difference observed in the results obtained by G.L.C. and C.I.E. is due to the fact that chemical species which are not measured by the former method can be determined by the latter one. T.L.C. analyses of bile acid extracts from axenic rats in which either a [26(-14C)] cholesterol or a [2,4(-3H)] cholic acid and [24(-14C)] chenodeoxycholic acid equilibrium were established, lead to the conclusion that the chemical composition of these undetermined substances is complex: part of these substances comes from the transformation of bile acids; another part is made of molecules which maintain the 26(-14C) of cholesterol.

[Action of the microbial flora of the digestive tract on the biosynthesis of cholic acid in the rat (author's transl)]

Axenic and holoxenic (conventional) rats were fed a diet containing trace amounts of [2,4-3H]cholic and [24-14C]chemodeoxycholic acids. In the feces of both groups of rats, the percentage of labelled bile acids which were 3H-labelled was slightly different. In the experimental conditions used, the intestinal microflora only slightly modified the synthesis of 12alpha-hydroxylated bile acids.

[Formation of omega-muricholic acid and fecal excretion of biliary acids in rats]

Two groups of Rats which were fed the same diet, excreted fecal bile acids of different patterns: in one group, the feces contained a large amount of omega-muricholic acid and very little hydrodeoxycholic acid; in the other group the reversed composition was observed. The first group excreted more total bile acids than the second. This observation suggests that the formation of a large amount of omega-muricholic acid results in an increase in total bile acid fecal excretion.

[The effect of dietary lactose on the ileal absorption of sodium taurocholate in rats]

When Rats were fed a lactose containing diet, both the absorption rate of sodium taurocholate at the level of ileum and the contents of bile acids of the small intestine were increased. On the contrary, feeding of lactose did not modify the daily fecal excretion of bile acids. It therefore appears that dietary lactose increases the intestinal pool of bile acids by increasing their ileal absorption rate and that this effect of lactose is not subordinated to a modification of bile acid synthesis.