Cellular Interactions and the Secondary Response <Emphasis Type="Italic">in vitro</Emphasis>

ALTHOUGH the role of cellular cooperation in the induction of the immune response has become firmly established only recently¹, morphological evidence suggesting that such cooperation takes place is quite old. Reports² of the aggregation of lymphoid cells around macrophages³ have been confirmed: “islets”, “rosettes” or “clusters” in cultures of cells (derived from humans⁴, guinea-pigs⁵, rabbits⁶ or mice⁷) stimulated with antigen or PHA⁸ were reported. We have investigated cluster formation to ascertain its relationship, if any, to the antigen-induced stimulation of sensitized cells⁹. We used peripheral blood leucocytes from rabbits immunized to bovine serum albumin (BSA) or to human red blood cells (HRBC). The BSA was given in complete Freund's adjuvant (three intramuscular injections of 7.5 mg BSA each, into the hind legs at weekly intervals). HRBC (1 ml.) was given once into the ear vein, as a 20% suspension in saline. Cell cultures and ³H-thymidine incorporation were measured as before¹⁰. To prepare cell smears, cells were washed three times and suspended in one drop of normal rabbit serum and 1 µl. of the suspension was spread on a microscope slide. This ensured a reasonably constant number of cells per slide and made possible comparisons between different experiments. Smears were fixed with methanol and stained with Giemsa.     

Reproductive traits of the freshwater oyster Etheria elliptica (Bivalvia: Etheriidae) in the Pendjari River,Benin: implications for conservation

The African freshwater oyster Etheria elliptica, which is of great economic importance throughout the continent, is facing overharvesting in many fisheries in West Africa. Its reproductive traits (sex ratio, size at sexual maturity, oocyte diameter and fecundity) were studied at four stations located along the Pendjari River, northern Benin, in April 2013. Histological techniques were implemented to identify sex and gonad development stages. Oocyte sizes were measured based on the histological images and mean oocyte diameter was 38 µm. Fecundity, estimated by counting the developing eggs, averaged 106 724 eggs and increased significantly with shell size. The average sex ratio was approximately 1:1. Hermaphrodites were rare. Males reached sexual maturity at 57.6 mm dorsoventral height, earlier than females at 64.7 mm. The majority of the oyster specimens were in ripe-spawning stages, indicating that reproductive activities partly took place towards the end of the dry season. Both mature and immature individuals were subjected to harvesting at all the investigated fishing sites. The mean size of exploited oysters was 60.6 mm, lower than the size of females at maturity. Management strategies must enforce the minimum size of 65 mm required for harvesting, particularly in open access sites where juveniles are mostly harvested.     

The California tumor registry

The California Tumor Registry, in which 71,215 cases have been entered, provides data for professional and public education which is specific to the state. It has suggested leads for epidemiological investigation of cancer. Participating agencies are assisted in maintaining adequate follow-up systems through annual listing of cases by the State Department of Public Health and removal from the list of cases in which death occurs. Among the first cases analyzed, the diagnosis was confirmed microscopically in 70.6 per cent. Only 36.2 per cent of patients had visited a physician within two months after onset of symptoms. Survival of patients with cancer is compared with their expectancy calculated from life-tables, thus taking account of deaths from causes other than cancer.     

Rheological properties of cross-linked hyaluronan-gelatin hydrogels for tissue engineering

Hydrogels that mimic the natural extracellular matrix (ECM) are used in three-dimensional cell culture, cell therapy, and tissue engineering. A semi-synthetic ECM based on cross-linked hyaluronana offers experimental control of both composition and gel stiffness. The mechanical properties of the ECM in part determine the ultimate cell phenotype. We now describe a rheological study of synthetic ECM hydrogels with storage shear moduli that span three orders of magnitude, from 11 to 3 500 Pa, a range important for engineering of soft tissues. The concentration of the chemically modified HA and the cross-linking density were the main determinants of gel stiffness. Increase in the ratio of thiol-modified gelatin reduced gel stiffness by diluting the effective concentration of the HA component.