[Development of the diaphragmatic muscle]. / Développement du muscle diaphragme.

Muscle biopsies were taken at the oesophageal opening and in the costal part of the diaphragm from 15 foetuses (aged between 11 and 40 weeks) and from four children aged 1 week, 5 months, 3 and 16 years. Subjects with multiple congenital abnormalities or neuromuscular diseases were not included in this study. Enzyme histochemistry (myosin ATPases) and immunohistochemistry using antibodies directed against vimentin, desmin, titin and different isoforms of the myosin heavy chains (MHCs) were carried out on serial frozen sections. The diameters of the different types of fibres were measured using a Leitz ASM 68K and the corresponding results were expressed either as mean values or as histograms. In both of the regions of the diaphragm which were examined (oesophageal opening and costal portion). The skeletal muscle fibres are formed from two successive generations in a manner very similar to that which we have previously described for the limb muscles. The chronology of the various events involved in the maturation of the diaphragm does however present certain distinctive features since the adult MHCs are expressed well before 30 weeks even though paradoxically large amounts of fetal MHC were still present at birth. These findings suggest the existence of a special regulatory mechanism in the diaphragm resulting either from its innervation by the phrenic nerve or from its specific functional constraints.

Chromatin structure and nucleic acid synthesis in human lymphocyte activation by phytohemagglutinin.

Alterations in chromatin structure were explored as a function of time following phytohemagglutinin (PHA) activation of human lymphocytes. Nuclear refringency (related to chromatin status), ultrastructural changes, and modifications of nucleic acid synthesis were compared. Chromatin dispersion was observed within 20 min of stimulation, with a concomitant increase in [3H]uridine incorporation; both were inhibited by actinomycin D. Recondensation of chromatin had occurred at 60 min when RNA synthesis was still increasing. The early chromatin dispersion thus was a reversible step and one of the most striking cellular events during the first phase of PHA activation. Late chromatin dispersion of blastic cells during the second phase of PHA response (after 24 h) was related to DNA synthesis in mitotic cells. This step was also inhibited by actinomycin D. These results suggest a relationship between the morphological changes in chromatin structure and the induction of RNA and DNA syntheses. The regulation of transcriptional and replicational states of the nucleus is discussed in terms of modifications of chromatin structure, considering PHA-induced calcium and cyclic nucleotide metabolism and interleukin II receptor expression.

The enhancement of interleukin 2 like production after in vivo stimulation of rat lymphoid cells by an acute non specific inflammatory process.

Interleukin 2 (IL 2) production was studied in lymphoid cells from rats undergoing an acute non specific inflammatory reaction induced by intrapleural injection of calcium pyrophosphate. Spleen and lymph node cells derived from inflamed animals had an increased level of IL 2 like production compared to cells from normal animals. Thymocytes also showed enhanced IL 2 like production although the absolute levels were lower than spleen or lymph node cells. It has been suggested that the acute non specific inflammatory reaction is able to modify lymphocyte reactivity via IL 2 and interleukin 1 (IL 1). The nature of the humoral factors released by the inflammatory process which are capable of initiating these events is also discussed.

Lymphocyte nuclear refringence in two inbred strains of rat. Modifications of NRT during adjuvant arthritis.

Nuclear refringence test (NRT) was studied in two inbred strains of rats: Lewis (LEW) and Wistar AG (WAG), the first develops a severe arthritis while the later only slight inflammation. Before adjuvant injection, a good NRT to ConA, PHA and Isoprinosine was observed in LEW but a poor one in WAG. After adjuvant injection a striking difference appears between the two strains concerning ConA response: in LEW the response is significantly lower on day 14, while in WAG the initial poor response is not modified. These data suggest that in WAG the suppressor T lymphocytes are already activated in vivo and are no longer responsive in vitro. The responses to PHA and Isoprinosine are parallel in both strains, the NRT response diminishes on day 14 in LEW and on day 21 in WAG.