Effect of prostaglandin E2 on agonist-stimulated cAMP accumulation in the distal convoluted tubule isolated from the rabbit kidney

The effects of calcitonin, vasoactive intestinal peptide (VIP), parathyroid hormone (PTH) and isoprenaline on intracellular cAMP accumulation were determined in the distal tubule (DCT) microdissected from collagenase-treated rabbit kidney. In DCTb (the initial bright portion) calcitonin (10 ng/ml) elicited a highly reproducible response 203.7±19.1 fmol cAMP mm^–1 4 min^–1 (SE, N=13) whereas VIP-induced cAMP accumulation was less and more variable from one experiment to another (1 M, 97.2±17.8 fmol mm^–1 4 min^–1, SE, N=12). When used in combination, these two agonists were non-additive, indicating stimulation of a single pool of cAMP in DCTb. In DCTg, (granular) which consists of at least two cell types, PTH (100 nM) elicited a marked, reproducible accumulation of cAMP (154.3±27.0 fmol mm^–1 4 min^–1; SE, N=5). Isoprenaline (1 M) and VIP (1 M) induced much smaller increases in cAMP levels 20.9±2.7 and 29.4±4.1 fmol mm^–1 4 min^–1 (SE, N=5) respectively, and, when used in combination, were non-additive, demonstrating that VIP and isoprenaline are active on the same cell type. In DCTb, prostaglandin E₂ (PGE₂) inhibited both calcitoninand VIP-stimulated cAMP accumulation (calcitonin 57.8±2.7% inhibition, SE, N=16; VIP, 80.6±2.1% inhibition, SE, N=5). The EC₅₀ values for calcitonin were 1.21±0.33 ng/ml and 1.83±0.25 ng/ ml (SD, N=3) in the absence and presence of PGE₂ (300 nM) respectively with an IC₅₀ for PGE₂ of 26.3±6.3 nM (SE, N=4). In contrast, no effects of PGE₂ were seen in DCTg vis à vis PTH, isoprenaline or VIP. The percentage inhibition of calcitonin-stimulated cAMP accumulation by PGE₂ was of the same order in the presence of isobutylmethylxanthine (an inhibitor of all types of phosphodiesterase), Ro 20-1724 (inhibitor of low-K _m cAMP-specific phosphodiesterase) or in the absence of inhibitor. Preincubation of DCTb with pertussis toxin for up to 8 h in different experimental conditions did not relieve the inhibition by PGE₂. Protein kinase C activation by phorbol ester did not attenuate calcitonin responses. These data demonstrate that the inhibition by PGE₂ of cAMP production is restricted to the initial portion (DCTb) of the distal convoluted tubule and is effective on both calcitonin and VIP responses. When tested in the presence of Ro 20-1724, ionomycin, A₁-adenosine, ₂-adrenergic and muscarinic agonists were without effect on calcitoninand PTH-stimulated cAMP accumulation in DCTb and DCTg respectively.     

Signal transduction in B lymphocytes

We have examined the activity and intracellular compartmentalization of protein kinase C (PKC) following activation of human B lymphocytes by anti-human leukocyte antigen (HLA) class II antibodies. 12-O-Tetradecanoylphorbol 13-acetate (TPA) treatment increased membrane-associated PKC (between five and nine times greater than the control value) and decreased cytosolic PKC (between 70% and 100% of the control value). In contrast, anti-class II antibodies induce an activation of PKC which results either in an increase of cytosolic activity or membrane-bound activity without redistribution of cytosolic PKC. The effect of TPA and HLA class II molecules on total PKC activity was comparable: when TPA induced an increase of total PKC activity so did HLA class II molecules and when TPA did not, HLA class II molecules did not. Measurement on SDS PAGE of histone phosphorylation confirmed the above results of PKC activity. Taken together, our results suggest that PKC might be implicated in HLA class II-induced B lymphocyte activation.     

Rejection of kidney graft: mechanism and prevention

Rejection occurs after the introduction of a genetically different graft, in a recipient. Nowadays, it is still a major obstacle in renal transplantation and reflects a normal protective immune response of a recipient against a foreign antigen. Involving many mechanisms of the innate and adaptive immunity, this reaction results in renal parenchymal lesions witch may progress to graft destruction and loss of its function. Several ways are currently used to reduce the action of the immune system and consequently reduce the risk of rejection. After a presentation of the main actors and the sequence of events leading to rejection, we will describe the strategy used by antirejection teams' transplantation. We will successively consider the prevention (pre-transplant immunological assessment, preventive immunosuppressive therapy), the monitoring (search for antibodies, biopsies) and the treatment.     

HLA polymorphism and early rheumatoid arthritis in the Moroccan population

ObjectivesRheumatoid arthritis (RA) is an autoimmune multifactorial disease which has a great socio-economic impact in Morocco. The association of HLA genes with RA was studied in various ethnic groups but not in the Moroccan population. Our study focused on evaluating the distribution of class I and class II HLA genes among Moroccan patients presenting early signs of RA.MethodsForty nine patients diagnosed with early RA were compared to a group of healthy controls matched by age, sex, and ethnic origin. Among the patient group, 34 were seropositive (presence of the rheumatoid factor). HLA typing of the patients and the controls was performed using microlymphocytotoxicity for class I (A and B) and PCR-SSP for class II (DR and DQ).ResultsWe found a significant increase of the frequency of the HLA-A24 antigen (p = 0.03), the DRB1*04 (p = 0.004) and DQB1*03 (p = 0.03) alleles and a significant decrease of the DRB1*07 allele (p = 0.03) in seropositive patients. The analysis of the frequency of the DRB1*01, DRB1*10, and DRB1*14 alleles did not show any difference between the RA patients and the controls. The frequency of DR4-DQ2 and DR4-DQ4 haplotypes was increased in the patients compared to the controls while that of DR7-DQ2 and DR13-DQ6 was decreased.ConclusionsOur study suggests that DRB1*04 predisposes to RA while DRB1*07 seems protective for the Moroccan patients population. In addition we show the influence of some haplotypes DR-DQ in the susceptibility and protection against the disease.