PubMed Health⌕ Search

Biomedical subjects

J Hiernaux

Publications and source records attributed to J Hiernaux.

10 recordsLinked to original sources
PubMed1992

On the kinetics and optimal specificity of cytotoxic reactions mediated by T-lymphocyte clones.

Using the chromium release assay and the single cell assay in agarose, we study the cytotoxic reaction of the MHC-restricted T lymphocyte clones P89:15 and P1:3, which recognize distinct but specific tumour antigens on the surface of syngeneic P815 mastocytoma cells. We propose a mathematical model which describes these experiments, accounts for the strongly non-Michaelian behaviour of the reaction and permits us to estimate the kinetic parameters characterizing effector-target conjugation and lethal hit delivery. The results show that the binding and lytic activity of effector cells is modulated by the number of targets bound to them. The binding of a second target by an effector having already a target bound is facilitated; on the other hand, an effector having bound two targets delivers a lethal hit more slowly than one with a single target bound. We investigate the role of these kinetic properties in the competition between the process of tumour progression due to cancer cell replication and the process of tumour regression due to T lymphocyte cytotoxic activity. For both clones, we estimate the effector-target ratio beyond which rejection prevails. This ratio is nine times larger for P1:3 than for P89:15. Furthermore, our analysis suggests that there exists an optimal specificity minimizing this ratio. Deviations from this optimum, be it in the sense of an increase or decrease of specificity, tends to stabilize the tumoural state: a situation which in the broader context of the immune response evolution and regulation can be viewed as an immune response dilemma.

Animals↗
PubMed1991

Refractory period phenomenon in the induction of tissue factor expression on endothelial cells.

Tissue factor (TF) is the first factor of the extrinsic pathway of coagulation. Normally, TF is not expressed on the surface of endothelial cells. However, expression of TF can be induced in these cells in response to stimulation by diverse inflammatory mediators such as interleukin-1 beta (IL-1 beta), tumor necrosis factor-alpha (TNF-alpha), lipopolysaccharide (LPS), and phorbol 12-myristate 13-acetate (PMA). We have studied the effect of these mediators on the kinetics of the induction of TF-related procoagulant activity (PCA) on human umbilical vein endothelial cells (HUVECs). PCA is transiently induced on HUVECs, attaining a peak some 4 to 8 hours after addition of inflammatory agents, with maximal accumulation of TF messenger RNA (mRNA) occurring 3 to 5 hours earlier. Because the expression of PCA by treated HUVECs returns to basal levels by 20 to 30 hours, we examined the response of these cells to a second inflammatory stimulus. Continuous incubation of cells with a single inflammatory agent for 24 to 48 hours induces a hyporesponsive state with respect to the reinduction of TF expression by the same agent (14% of the initial stimulation for IL-1 beta, 39% for TNF-alpha 30% for LPS, and 7% for PMA). Such a diminution in PCA was also observed in the levels of TF mRNA. By contrast, pretreatment of HUVECs with one agent did not dramatically affect the reinduction of TF by any of the three other factors. We subsequently focused our attention on the induction of the autologous refractory period by IL-1 beta. De novo protein synthesis was not required during the preincubation of ECs for hyporesponsiveness to be observed. The establishment of the refractory state did not depend on the downmodulation of IL-1 beta receptor affinity or expression. Moreover, pretreatment of HUVECs with IL-1 beta increased prostacyclin (PGI2) production in response to a second stimulation by IL-1 beta, although such cells were unable to reexpress TF under the same conditions. This result suggests that distinct secondary messenger pathways are involved in TF induction and PGI2 synthesis by IL-1 beta in HUVECs.

Endothelium, Vascular↗
PubMed1979

Anthropometric differences between sicklers and nonsicklers in Zairian adults.

From a sample of 1,079 male adult Zairians living in regions where falciparum malaria is endemic 212 sicklers and 867 nonsicklers were compared for eight anthropometric variables. The two groups did not differ significantly in their variances. The sicklers had a higher mean for seven variables, but significantly so for head breadth only. These results are discussed in terms of the balance of the possible effects of the AS genotype on growth and of the possible selective effects of death from malaria in infancy.

Adult↗
PubMed1976

A model for competing polymers leading to their spatial separation.

A model for a prebiotic polymer synthesis in a gradient of monomer is presented. In the absence of mutations the synthesis of the polymer proceeds in the region where the monomer concentration is the highest. However if a favorable mutation occurs, the latter accumulates in the high concentration zone and the initial polymer is restricted to a poorer monomer concentration region.

Biological Evolution↗
PubMed1976

Blood polymorphism frequencies in the Sara Majingay of Chad.

Blood samples of 258 Sara Majingay of Ndila (Southern Chad) were analysed. Phenotype and allele frequencies are given for 22 polymorphisms. For each of these, the Majingay are compared to a number of other African populations. Then they are included in a set of 8 African populations between which multivariate distances for 25 alleles at 9 loci are computed. A two-dimensional representation is derived from the matrix of distances, and is discussed. It bears the stamp of gene flow in central Ethiopia, where an Arab admixture is evident, and in Southern Africa, where a reciprocal gene flow has marked the gene pools of Khoisan and Bantu speakers to a varying degree. The Majingay stand relatively near to the Bedik, another population of West-Central Africa. The non-Arab or non-Khoisan components of the gene pool of the other populations do not seem to differ largely from the gene pools of the West-Central African populations.

Acid Phosphatase↗
PubMed1975

Model for the positional differentiation of the cap in Acetabularia.

A late stage during the biological cycle of the unicellular alga Acetabularia is the differentiation of a cap at the apical end of the stalk. A minimal model of the spatio-temporal regulation of this event is proposed on the basis of biological data available and current hypotheses. This involves the interaction between a diffusing inhibitor specific to the translation of cap mRNAs and a graded distribution of these messengers. The model accounts for delayed protein synthesis which occurs preferably at the apex and is likely to initiate the formation of the cap. The biological and theoretical implications are discussed.

Acetabularia↗