Distribution and antimicrobial susceptibility of bacteria from adults with community-acquired pneumonia or complicated skin and soft tissue infections in France: the nationwide French PREMIUM study.

The empirical therapy of community-acquired pneumonia (CAP) and complicated skin and soft tissue infections (cSSTIs) must be based on updated bacterial distribution and susceptibility data. A nationwide study consecutively collected 1288 isolates from CAP (n=467) and cSSTIs (n=821) from 18 French hospitals between 2012 and 2013. The MIC values of commonly used antimicrobial agents, including ceftaroline, were determined. Bacterial distribution featured Pneumococcus, Haemophilus influenzae, and Staphylococcus aureus for CAPs and S. aureus, ß-hemolytic streptococci and Enterobacteriaceae for cSSTIs. Antimicrobial susceptibility testing indicated i) the sustained third-generation cephalosporins and levofloxacin activity against pneumococci and H. influenzae, ii) no methicillin-resistant Staphylococcus aureus emergence among respiratory pathogens, iii) the high in vitro activity of ceftaroline against staphylococci from cSSTIs (98.7% susceptibility), and iv) the worrisome decreasing fluoroquinolone and third-generation cephalosporin susceptibilities among Enterobacteriaceae. This laboratory-based survey depicts a contrasting situation and supports the scoring of patients for the resistant pathogen risk before empirical therapy.

[Impact of enterobacteriaceae-producing extended-spectrum beta-lactamases (ESBLE) incidence increasing on barrier precautions implementation in a university hospital]. / Impact de l'augmentation de l'incidence des entérobactéries productrices de bêta-lactamases à spectre étendu (EBLSE) sur l'application des précautions complémentaires dans un centre hospitalier universitaire.

AIM OF THE STUDY: The French national surveillance program of multidrug-resistant bacteria (MDR) shows an increase of enterobacteriaceae-producing extended-spectrum beta-lactamases (ESBLE) incidence. The objectives of this study were to assess: the incidence of EBLSE in a large French university hospital between 2005 and 2010, and the difference of barrier precautions implementation between ESBL and other MDR. METHODS: The ESBLE incidence measure used data from the laboratory of bacteriology. The application of isolation and barrier precautions was analyzed from the MRB national surveillance data over a 3-year period from 2006 to 2008. Data were entered and analyzed using Epi Info software. The Chi(2) test was used for the comparison of proportions. RESULTS: The overall incidence of ESBLE was significantly higher in 2010 than in 2005 (0.20/1000 patients-days vs 0.03/1000 patients-days, respectively) (P<0.001). The same was observed for Escherichia coli incidence with rates ranging from 0.02/1000 patients-days in 2005 to 0.15/1000 patients-days in 2010. Isolation precautions for patients with EBLSE were applied in relation for most patients with MRB (ESBLE vs others), without significant difference. CONCLUSION: The surveillance programme of MRB showed a significant increase of ESBLE, especially for E. coli. Isolation and barrier precautions were used for most patients with MRB, including ESBLE.

Ataxin-7 interacts with a Cbl-associated protein that it recruits into neuronal intranuclear inclusions.

Spinocerebellar ataxia 7 (SCA7) is a neurodegenerative disease caused by expansion of a CAG repeat in the coding region of the SCA7 gene. The disease primarily affects the cerebellum and the retina, but also many other central nervous system (CNS) structures as the disease progresses. Ataxin-7, encoded by the SCA7 gene, is a protein of unknown function expressed in many tissues including the CNS. In normal brain, ataxin-7 is found in the cytoplasm and/or nucleus of neurons, but in SCA7 brain ataxin-7 accumulates in intranuclear inclusions. Ataxin-7 is expressed ubiquitously, but mutation leads to neuronal death in only certain areas of the brain. This selective pattern of degeneration might be explained by interaction with a partner that is specifically expressed in vulnerable cells. We used a two-hybrid approach to screen a human retina cDNA library for ataxin-7-binding proteins, and isolated R85, a splice variant of Cbl-associated protein (CAP). R85 and CAP are generated by alternative splicing of the gene SH3P12 which we localized on chromosome 10q23-q24. The interaction between ataxin-7 and the SH3P12 gene products (SH3P12GPs) was confirmed by pull-down and co-immunoprecipitation. SH3P12GPs are expressed in Purkinje cells in the cerebellum. Ataxin-7 colocalizes with full-length R85 (R85FL) in co-transfected Cos-7 cells and with one of the SH3P12GPs in neuronal intranuclear inclusions in brain from a SCA7 patient. We propose that this interaction is part of a physiological pathway related to the function or turnover of ataxin-7. Its role in the pathophysiological process of SCA7 disease is discussed.

RLIP76, an effector of the GTPase Ral, interacts with the AP2 complex: involvement of the Ral pathway in receptor endocytosis.

RLIP76 is a modular protein that was identified as a putative effector of Ral, a GTPase activated during Ras signaling. To explore further the contribution of the Ral-RLIP76 pathway to Ras signaling, we have looked for partners of RLIP76. Mu2, the medium chain of the AP2 complex is shown to interact with RLIP76. We show also that in vivo endogenous AP2 and RLIP76 form a complex and that this in vivo interaction is independent of cells being stimulated by a growth factor. Furthermore, RLIP76 differentiates AP2 from AP1 in vivo as RLIP76 differentiates mu2 from mu1 in vitro and in two hybrid assays. We show that activated Ral interferes with both tranferrin receptor endocytosis and epidermal growth factor (EGF) receptor endocytosis in HeLa cells. We propose a model where the Ral-RLIP76 pathway connects signal transduction and endocytosis through interaction on one hand between the Ras-Ral pathway and RLIP, on the other hand between RLIP and proteins belonging to the endocytotic machinery.

Nitric oxide and l-arginine cause an accumulation of utrophin at the sarcolemma: a possible compensation for dystrophin loss in Duchenne muscular dystrophy.

Duchenne muscular dystrophy (DMD), a severe X-linked recessive disorder which results in progressive muscle degeneration, is due to a lack of dystrophin, a membrane cytoskeletal protein. An approach to treatment is to compensate for dystrophin loss with utrophin, another cytoskeletal protein with over 80% homology with dystrophin. Utrophin is expressed, at the neuromuscular junction, in normal and DMD muscles and there is evidence that it may perform the same cellular functions as dystrophin. So, the identification of molecules or drugs that could up-regulate utrophin is a very important goal for therapy. We show that in adult normal and mdx mice (an animal model of Duchenne myopathy) treated with l-arginine, the substrate of nitric oxide synthase (NOS), a pool of utrophin localized at the membrane appeared and increased, respectively. In normal and mdx myotubes in culture, l-arginine, nitric oxide (NO), or hydroxyurea increased utrophin levels and enhanced its membrane localization. This effect did not occur with d-arginine, showing the involvement of NOS in this process. The NO-induced increase in utrophin was prevented by oxadiazolo-quinoxalin-1-one, an inhibitor of a soluble guanylate cyclase implicated in NO effects. These results open the way to a potential treatment for Duchenne and Becker dystrophies.

Nitric oxide transforms serotonin into an inactive form and this affects neuromodulation.

Nitric oxide is a highly reactive molecule, diffusible and therefore ubiquitous in the central nervous system. Consequently, nitric oxide or nitric oxide-derived nitrogen oxides must enter into contact with neuromodulators and they can modify these molecules, especially monoamines, and thus change their regulatory action on synaptic transmission. We tested this possibility on a well-known, identified cholinergic synapse of Aplysia buccal ganglion, in which we have found that evoked acetylcholine release was decreased by extracellularly applied serotonin. We show that this modulatory effect of serotonin was largely reduced not only in the presence of 3-morpholinosydnonimine, a nitric oxide donor, but also when endogenous nitric oxide synthase was activated. We have shown that this decrease in the serotonin effect is due to the formation of chemical derivatives of serotonin, mainly a symmetric serotonin dimer, 4-nitroso-serotonin and 4-nitro-serotonin, which are ineffective in reproducing the modulatory effect of serotonin. Serotonin is involved in the regulation of several central functions, such as sleep-wake activity or mood. The consequences of chemical modifications of serotonin by nitric oxide must be taken into account in physiological as well as pathological situations. In addition, our results highlight the importance of the physiological implications of interactions between free radicals and neuromediators in the nervous system.

A Sos-derived peptidimer blocks the Ras signaling pathway by binding both Grb2 SH3 domains and displays antiproliferative activity.

With the aim of interrupting the growth factor-stimulated Ras signaling pathway at the level of the Grb2-Sos interaction, a peptidimer, made of two identical proline-rich sequences from Sos linked by a lysine spacer, was designed using structural data from Grb2 and a proline-rich peptide complexed with its SH3 domains. The peptidimer affinity for Grb2 is 40 nM whereas that of the monomer is 16 microM, supporting the dual recognition of both Grb2 SH3 domains by the dimer. At 50 nM, the peptidimer blocks selectively Grb2-Sos complexation in ER 22 (CCL 39 fibroblasts overexpressing epidermal growth factor receptor) cellular extracts. The peptidimer specifically recognizes Grb2 and does not interact with PI3K or Nck, two SH3 domain-containing adaptors. The peptidimer was modified to enter cells by coupling to a fragment of Antennapedia homeodomain. At 10 microM, the conjugate inhibits the Grb2-Sos interaction (100%) and MAP kinase (ERK1 and ERK2) phosphorylation (60%) without modifying cellular growth of ER 22 cells. At the same concentration, the conjugate also inhibits both MAP kinase activation induced by nerve growth factor or epidermal growth factor in PC12 cells, and differentiation triggered by nerve growth factor. Finally, when tested for its antiproliferative activity, the conjugate was an efficient inhibitor of the colony formation of transformed NIH3T3/HER2 cells grown in soft agar, with an IC50 of around 1 microM. Thus, the designed peptidimers appear to be interesting leads to investigate signaling and intracellular processes and for designing selective inhibitors of tumorigenic Ras-dependent processes.

A new member of the amphiphysin family connecting endocytosis and signal transduction pathways.

Src homology 3 (SH3) domains are conserved modules which participate in protein interaction by recognizing proline-rich motifs on target molecules. To identify new SH3-containing proteins, we performed a two-hybrid screen with a proline-rich region of human SOS-1. One of the specific SOS-1 interacting clones that were isolated from a mouse brain cDNA library defines a new protein that was named amphiphysin 2 because of its homology to the previously reported amphiphysin. Amphiphysin 2 is expressed in a number of mouse tissues through multiple RNA transcripts. Here, we report the amino acid sequence of a brain form of amphiphysin 2 (BRAMP2) encoded by a 2. 5-kilobase mRNA. BRAMP2 associates in vitro with elements of the endocytosis machinery such as alpha-adaptin and dynamin. On a biosensor surface, the BRAMP2/dynamin interaction appeared to be direct and partly dependent on a proline-rich sequence of dynamin. Association with dynamin was also observed in PC12 cells after cell stimulation with nerve growth factor, suggesting that amphiphysin 2 may be connected to receptor-dependent signaling pathways. This hypothesis is strengthened by the ability of BRAMP2 to interact with the p21(ras) exchange factor SOS, in vitro, as a possible point of interconnection between the endocytic and signaling pathways.

B cell antigen receptor-mediated apoptosis. Importance of accessory molecules CD19 and CD22, and of surface IgM cross-linking.

Engagement of the B cell Ag receptor can induce a suicide pathway in various B cell types. Earlier studies showed that anti-IgM mAb treatment triggers apoptotic death in the Burkitt lymphoma-derived cell line, Ramos. We show that two B cell surface molecules, CD19 and CD22, which have been reported to interact either functionally or structurally with the B cell Ag receptor, also stimulate cell suicide when sufficiently aggregated, both in the Ramos and EBV-infected Ramos AW cell lines. In conditions of lower cross-linking, both molecules enhance the apoptotic response induced by a suboptimal dose of anti-IgM mAb in Ramos cells, reinforcing the notion that CD19 and CD22 may be involved in the death pathway and modulate Ag-induced B cell apoptosis. Similar outcomes were obtained with human tonsillar B cells, which enter the death program upon treatment with cross-linked anti-IgM, -CD19, or -CD22 mAbs. These results indicate that Ag-induced B cell suicide may affect mature B cells in the periphery and may be regulated via the interaction of CD19 and/or CD22 with their respective ligand(s). Early tyrosine phosphorylations were analyzed by Western blotting. The biologic outcome of these various treatments--cell survival or death--could not be related to any detectable new tyrosine-phosphorylated substrate, further questioning the biochemical basis of apoptosis signaling.

CD22 associates with the human surface IgM-B-cell antigen receptor complex.

The B-cell surface molecule CD22, when cross-linked, modulates signaling through the surface IgM (sIgM)-B-cell receptor (BCR) complex. Here we analyzed the basis of this interaction between CD22 and the human sIgM complex. After lysis of B cells or B-cell lines in digitonin, CD22 coimmunoprecipitated a kinase activity that in vitro-phosphorylated two polypeptides of 150 and 130 kDa on tyrosine residues. By immunoblot analysis with a rabbit anti-serum specific for a synthetic peptide of CD22, we found these proteins to be CD22 itself. Furthermore, the phosphorylated 150-kDa CD22 was found in the sIgM-BCR complex maintained by digitonin, along with Ig alpha/mb-1, Ig beta/B29, and a 75-kDa polypeptide precipitated by an antiserum specific to protein-tyrosine kinase PTK72. CD22 is likely to be an important signaling partner in the sIgM-BCR complex since it is very rapidly and strikingly phosphorylated after sIgM is cross-linked and since it contains the antigen recognition homology I (ARHI) motif, present in other antigen receptor molecules.

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.

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.

B- and T-cell activation in the thymus of patients with myasthenia gravis.

The activation state of thymic T and B lymphocytes was phenotypically and functionally explored in patients with Myasthenia Gravis (MG). We detected no phenotypic signs of activation in fresh total thymic lymphocyte suspensions (CD25 expression) while functional signs of activation were reflected by a significantly higher sensitivity to recombinant IL-2 (rIL-2) without any previous stimulation in MG patients as compared to controls. The response to rIL-2 was time-and dose-dependent, was inhibited by a blocking anti-IL-2 receptor antibody, and was associated to an increase of CD25+ T cells. Thymic B-cell populations purified after T cell and macrophage depletion, expressed at variable levels activation markers such as the transferrin receptor, the CD25, 4F2, CD23 and B8.7 Ag, indicating that a marked proportion of them are activated. Moreover, these B-cell populations were spontaneously sensitive to BCGF-12-kD and to a lesser extent to rIL-2, demonstrating that they also exhibit functional signs of activation. The largest proportion of activated B cells and the most intense response to BCGF-12-kD was found in patients presenting the highest anti-acetylcholine receptor (AChR) titers. Our data confirm the hyperactivity of the thymus gland in MG, reflected by the presence of T and B cells with functional signs of pre-activation. These cells could conceivably be located in lymphoid follicles and may represent autoreactive cells involved in the autoimmune process. Whether they are sensitized to AChR remains to be investigated.

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.