Administration of IL-7 to normal mice stimulates B-lymphopoiesis and peripheral lymphadenopathy.

Normal mice were injected with IL-7 (500 ng, twice daily) for various periods of time up to 6 days and the cellularity and phenotypic composition of the thymus, spleen, lymph node, and bone marrow was assessed. After 6 days of treatment, significant increases in the cellularity of the spleen, lymph node, and bone marrow were observed which returned to the normal range within 6 days after cessation of treatment. After 3 days of IL-7 treatment, increased numbers of B220+/surface(s) IgM- bone marrow cells were observed. After 6 days of treatment, these numbers were still further increased and a significant population of B220+/sIgM- cells were observed in the spleen. The numbers of c mu+/sIgM- cells were also increased in the IL-7-treated mice. Analysis of the expression of B220 and BP-1 on the sIgM- bone marrow cells revealed that the B220+/BP-1+ population was dramatically increased after IL-7 treatment and the size of the B220+/BP-1- population did not differ from control mice. The pre-B cell numbers declined rapidly after the cessation of IL-7 treatment. After 6 days of IL-7 treatment, a twofold increase in the number of B cells in the spleen and lymph node was observed. The B cell numbers declined to normal values within 6 days after the cessation of IL-7 administration. In the spleens of the IL-7-treated mice, there was a significant increase in the number of B cells with an immature phenotype (e.g., sIgMhi/sIgDlo, decreased levels of Ia and FcR expression). The numbers of CD8+ and CD4+ T cells were also increased in the lymph node and spleen of the IL-7-treated mice. These numbers declined to normal levels after the cessation of IL-7 treatment.     

Modelling of concentration profiles in tower fermenter. The influence of the axial dispersion coefficient

The production of CO₂ in tower fermenters which can cause back mixing, and thereby reducing the efficiency of such fermenters has been modelled with respect to fermentation. It is confirmed that the effect is significant. The effect of variations in the kinetic parameters, the maximum specific growth rate and the biomass yield coefficient was found to be insignificant. A good correlation between experimental and calculated data was obtained.     

MECHANISMS OF AVIAN IMPRINTING: A REVIEW

Filial imprinting is the process through which early social preferences become restricted to a particular object or class of objects. Evidence is presented showing that filial preferences are formed not only as a result of learning through exposure to an object, but also under the influence of visual and auditory predispositions. The development of these predispositions is dependent upon certain non-specific experience. There is little evidence for an endogenously affected sensitive period for imprinting. It is more likely that the end of sensitivity is a result of the imprinting process itself. Similarly, it is now firmly established that filial and sexual preferences are reversible. Evidence suggests, however, that the first stimulus to which the young animal is exposed may exert a greater influence on filial preferences than subsequent stimuli. The learning process of imprinting is often regarded as being different from conventional associative learning. However, the imprinting object itself can function as a reinforcer. Recent studies have attempted to test predictions from an interpretation of filial imprinting as a form of associative learning. The first results suggest that ‘blocking’ may occur in imprinting, whilst there is no evidence for ‘overshadowing’. Social interactions with siblings and parent(-surrogates) have been shown to affect the formation of filial and sexual preferences. The influence of these interactions is particularly prominent in sexual imprinting, making earlier claims about naive species-specific biases unlikely. Although auditory stimuli play an important role in the formation of social attachments, there is little evidence for auditory imprinting per se. Auditory preferences formed as a result of mere (pre- or postnatal) exposure are relatively weak and short-lasting. Exposure to visual stimuli during auditory training significantly improves auditory learning, possibly through a process of reinforcement. It is becoming increasingly clear that filial and sexual imprinting are two different (although perhaps analogous) processes. Different mechanisms are likely to underlie the two processes, although there is evidence to suggest that the same brain region is involved in recognition of familiar stimuli in both filial and sexual imprinting. There is little evidence for a direct role of hormones in the learning process of imprinting. Androgen metabolism may be a factor constraining the development of a predisposition in the chick. Research into the neural mechanism of filial imprinting in the chick has revealed that a restricted part of the forebrain (IMHV) is likely to be a site of memory storage. Changes in synapse morphology and in the number of NMDA receptors have been found, limited to this region, and correlated with the strength of preference.     

The cytoplasmic tail of CD4 targets chimeric molecules to a degradative pathway.

Many different cell surface receptors undergo endocytosis via coated pits. Once having entered the cell, the receptors are sorted into diverse pathways. Which path a given receptor will follow is determined by signals inherent in the receptor's structure. The nature of these structural features is not yet known. In this study, we have taken the approach of constructing chimeric molecules to localize the domain of the T-cell surface molecule CD4 which is responsible for targeting it for degradation. Chimeric molecules bearing the cytoplasmic domain of CD4 and the extracellular domain of either the low-density lipoprotein receptor or a major histocompatibility complex (MHC) class I molecule were both internalized in response to phorbol 12-myristate 13-acetate and were subsequently degraded, indicating that the cytoplasmic tail of CD4 contains all the information required for both processes. The ability to modulate the level of MHC class I molecules on the cell surface offers an approach to investigating quantitative aspects of antigen presentation, the initial possibilities of which are explored herein.     

Sources of plant sterol contaminants encountered in low level steroid analysis

During development of an analytical method to characterize ligands to new members of the steroid hormone receptor superfamily, a persistant contaminant profile was observed during gas chromatographic analysis of reagent blanks. Mass spectrometric analysis identified three of the contaminant peaks as cholesterol and the plant sterols stigmasterol and sitosterol. Laboratory articles made of natural rubber, i.e. pipette fillers and latex gloves, were found to be the source of these and other compounds in the reagent blank profile.