Recombinant 25-kDa CD23 and interleukin 1 alpha promote the survival of germinal center B cells: evidence for bifurcation in the development of centrocytes rescued from apoptosis.

Germinal centers contain a proliferating pool of centroblasts which give rise to non-dividing centrocyte. Centrocytes are programmed to die by apoptosis unless they receive a positive signal for rescue. Rescue, in vivo, is likely to be dependent, initially, on interaction with antigen held on follicular dendritic cells (FDC). A subset of FDC located in that part of the germinal center furthest from centroblasts is particularly rich in CD23. Supernatants containing high levels of soluble CD23 were found not only to encourage the survival of germinal center B cells but also to promote their differentiation toward a plasmacytoid morphology; these activities were diminished following removal of CD23 from the supernatants. Recombinant 25-kDa CD23 was initially found to be incapable of providing the signal for germinal center cell development but on the addition of interleukin 1 alpha which, by itself, was inactive, rescue and differentiation of germinal center B cells were now achieved. Apoptosis in germinal center cells could also be prevented by the ligation of surface CD40 with monoclonal antibody: however, rescue via this pathway was not accompanied by plasmacytoid differentiation. These findings provide a functional rationale to the high level expression of CD23 found within a discrete subset of FDC and indicate a bifurcation in the development of germinal center B cells following their rescue from apoptosis.     

Similar CD40 ligand expression on EL-4 thymoma cell lines with widely different helper activity for B lymphocytes.

A mutagenized subclone of the murine EL-4 thymoma (clone B5) is approximately 30 times more potent than parental EL-4 cells in stimulating proliferation and Ig secretion of murine or human B cells by direct cell contact in the presence of appropriate cytokines. In this study we found that CD40 ligand (CD40L) expression was constitutive and very similar on EL-4 B5 and parental EL-4 cells according to Northern blot and flow cytometry. Activation with phorbol 12-myristate 13-acetate (PMA) alone, PMA and ionomycin, interleukin-1 (IL-1) or human T-cell supernatant did not lead to significant CD40L up-regulation. A receptor-binding assay with soluble CD40 did not reveal different ligand affinities. However, murine and human soluble CD40-IgFc fusion proteins inhibited human B-cell stimulation by EL-4 B5 cells in the presence of human T-cell supernatant. Inhibition was 96% when soluble CD40 was added on day 0 of culture and progressively decreased when the CD40 was added subsequently. Ig secretion by cytoplasmic Ig-positive cells was no longer inhibited. These findings imply that, although CD40 ligand is necessary for B-cell activation by EL-4B5 cells, additional molecule(s) must be responsible for the increased helper activity of the EL-4 B5 clone.     

Prospective randomized study of St Jude Medical versus Bj?rk-Shiley or Starr-Edwards 6120 valve prostheses in the mitral position. Three hundred and fifty-seven patients operated on from 1979 to December 1983

During a 5 year period (January 1979-December 1983) 357 patients were submitted to mitral valve replacement. These were performed by the same surgeon and were randomized in 2 groups: Group A consisted of 179 patients who received a St Jude Medical (SJM) prosthesis in the mitral position. Group B comprised 178 patients with a Bj?rk-Shiley valve (BSM) initially (113 patients from 1979 to December 1981 matched with 111 SJM) and later a Starr-Edwards 6120 valve prosthesis (65 patients matched with 63 SJM). Analysis of 21 preoperative clinical, hemodynamic data and operative variables showed the groups to be well randomized. All patients were anticoagulated postoperatively. A follow-up study was performed each year postop: at the end of 1986 there was a 35 to 95 months follow-up with a mean of 64.7 months (1596 patient years follow-up). Fifteen patients were lost to follow-up. There were 8.4% deaths related to the prosthesis in group A and 20.2% in group B (p less than 0.001). The difference was due mainly to deaths from thromboembolic complications and sudden deaths. The rate of peripheral arterial embolic complications was 2.3% in group A and 4.3% in group B per patient year (NS). The difference between the 2 groups is significant for all thromboembolic events including sudden deaths: 3.1% in group A and 7.9% per patient year in group B (p less than 0.001). There were no statistical differences in the rates of endocarditis per patient year (0.3% in group A, 0.9% in group B), reoperation (0.75% in group A, 0.89% in group B), or anticoagulant related hemorrhage (1.6% in group A, 2.4% in group B). Actuarial survival rate, including all postoperative deaths, is significantly different (p less than 0.05) at 5 years, 87.6% +/- 4.5 (group A) versus 77.4% +/- 6 (group B) and at 7 years follow-up, 83.4% +/- 6.5 (group A) versus 73.2% +/- 7.2 (group B). The probability of freedom from death and complications related to the prosthesis is significantly different (p less than 0.001) at 5 years postoperatively: 79% +/- 6.5 for group A versus 54% +/- 7.5 for group B and at 7 years: 72% +/- 7.5 (group A) versus 46% +/- 8.5 (group B). Comparison of subgroups, 113 BSM versus 111 SJM (1979-81) and 65 SE 6120 versus 63 SJM (1982-83) showed similar significant differences in the results: however there were more early deaths, valve thrombosis, valve dysfunctions and sudden late deaths in the BSM group and more peripheral arterial emboli in the SE 6120 group.(ABSTRACT TRUNCATED AT 400 WORDS)     

Charge heterogeneity of beta 2-microglobulin in lymphoid cells

Extracts of blood lymphocytes, polymorphonuclear neutrophils and B, T or monocytic cell lines were analyzed by two-dimensional gel electrophoresis and immunoradiometric assay after electro-transfer to nitrocellulose sheets with radiolabelled polyclonal or monoclonal antibodies specific for beta 2-microglobulin. Four different forms of the molecule were identified with an apparent Mr of 12,000 and pI values of 5.7, 5.3 and lower. Lymphocyte activation by phytohemagglutinin and concanavalin A, or incubation with recombinant alpha 2b interferon, resulted in an increased beta 2-microglobulin cell content and release of the protein in supernatants with a predominant elevation of the more acidic minor forms. Recombinant interleukin-2 and recombinant gamma interferon increased the expression of the molecule without significant shift in the relative proportion of beta 2-microglobulin forms. Tumor necrosis factor alpha did not increase cell beta 2-microglobulin (beta 2-m) content and release and did not alter the relative distribution of the different forms of the molecule. Several mechanisms may be considered for the generation of beta 2-m microheterogeneity, including intracytoplasmic post-translational modifications such as proteolysis or modification of the amide groups of internal amino acids.     

Acute pancreatitis and biochemical markers. Isoamylase

Amylase activity in blood and urine, lipase activity in blood, and amylase/creatinine clearance ratio have been prospectively compared in order to test these parameters against estimation of pancreatic isoamylase. Pancreatic isoamylase had been evaluated by inhibition methodology and not by electrophoresis. One hundred patients admitted for strictly sus-umbilical abdominal pain in emergency unit have been studied. Results show that we do not have in blood specific biochemical marker for acute pancreatitis. Lipase and P isoamylase activity evaluation have about the same specificity. In emergency situation the choice of routine investigation will be rather based on methodological simplicity and lower cost.     

Optic fibre as a transducer of tendomuscular forces

Direct in vivo tendon force measurements open up new possibilities for understanding of muscletendon loads during natural locomotion. The present report presents a new optic fibre method for such applications. The method is based on light intensity modulation by mechanical modification of the geometric properties of the optic fibre. A special optic fibre with a plastic covering buffer and with a total diameter of either 265 m or 500 m was carefully prepared at both ends for receiving and transmitting light. The fibre was inserted through the rabbit common calcaneal tendon with a 20 gauge needle. By removing the needle the optic fibre remained in situ. Static loading demonstrated that the voltage output of the optic fibre transducer showed a good linear fit of r =.999 with added loads. In dynamic loading conditions the optic fibre followed well the response of a strain gauge transducer, which was also attached to the tendon. The optic fibre method seems suitable for many applications for tensile and possibly ligament force measurements.     

Plasmodium falciparum AARP1, a giant protein containing repeated motifs rich in asparagine and aspartate residues, is associated with the infected erythrocyte membrane.

During Plasmodium falciparum asexual intraerythrocytic development, the host's cell plasma membrane is modified by the insertion of parasite proteins. One or more of these modifications mediate the cytoadherence of infected erythrocytes to host vascular endothelium. However, these surface antigens can be the target of cytophilic antibodies which promote phagocytosis of the infected erythrocyte. It has been proposed that antibodies directed to epitopes rich in asparagine play an important role in this process, which has promoted efforts to isolate the corresponding gene(s). We describe here P. falciparum asparagine- and aspartate-rich protein 1 (PfAARP1), a new giant (circa 700-kDa) protein associated with the infected erythrocyte membrane which is rich in asparagine and aspartate residues due to the presence of nine blocks of repeats. Topology analysis predicts that PfAARP1 has multiple transmembrane domains and at least five external loops. Human antibodies immunopurified against a sequence composed exclusively of asparagine and aspartate amino acids derived from PfAARP1 label the surface of the infected erythrocyte, demonstrating that such motifs are exposed. Interestingly, external loop 4 of PfAARP1 contains repetitions of these residues, and their possible role as a target of cytophilic antibodies is discussed.