B precursor cell

If the damage is to the bone marrow where all the blood cells develop, this causes pancytopenia. In this case, both T- and B-precursor cells are damaged so that the system is compromised as well as other blood cells, including neutrophils. 

Fig. 2. Estimation of frequency of B precursor cells specific for SRC (redrawn from Cudkowicz et al., 1970). Symbols indicate observed percentages and the curve expected percentages according to the Poisson distribution. About 3X10 cells correspond to 63% positive spleens / = 3.3 x 10 )...

Homing efficiency has already been discussed in the section on the splenic foci technique. The estimates for the fraction of specific cells which lodged in the spleen was in the range of 4-15% (see Chapter A). In experiments on transfer of an anti-DNP clone, Askonas et al. (1972) estimated the effective homing of B precursor cells in the spleen to be around 1 %. 

With an input of 2X10 spleen cells per microculture in 12 experiments (about 2600 microcultures) 12-75% non-responding microcultures were obtained (Lefkovits, 1972). In these experiments, spleen cells from ordinary mice were used. Hence, it could not be shown unequivocally that any nonresponding culture was lacking only one type of cell—the B precursor cell. 

Table 7- Killing of B-precursor cells by specific lethal radioactive antigens (suicide experiment). From Hasten et al. (1971)...

Labastie MC, Cortes F, Romeo PH, Dulac C and Peault B (1998). Molecular identity of hematopoietic precursor cells emerging in the human embryo. Blood 92 3624-3635. 

The anaemia in B deficiency is caused by an inability to produce sufficient of the methylating agent S-adenosyhnethionine. This is required by proliferating cells for methyl group transfer, needed for synthesis of the deoxythymidine nucleotide for DNA synthesis (see below and Chapter 20). This leads to failure of the development of the nucleus in the precursor cells for erythrocytes. The neuropathy, which affects peripheral nerves as well as those in the brain, is probably due to lack of methionine for methyl transfer to form choline from ethanolamine, which is required for synthesis of phosphoglycerides and sphingomyelin which are required for formation of myelin and cell membranes. Hence, the neuropathy results from a... 

The IL-3 receptor is found on a wide range of haematopoietic progenitor cells (see Chapter 6). They are also present on monocytes and B lymphocytes. Its major biological activity relates to stimulation of growth of various cell types derived from bone marrow cells and which represent the immature precursors to all blood cells (Chapter 6). IL-3 thus appears to play a central role in stimulating the eventual formation of various blood cell types, in particular monocytes, mast cells, neutrophils, basophils and eosinophils, from immature precursor cells in the bone marrow. Several other cytokines (including IL-2, -4, -5, -6, -7, -11, -15 and CSFs) also play important costimulatory roles in the maturation of the range of blood cells. 

Craig, C.G., Tropepe, V., Morshead, C.M., Reynolds, B.A., Weiss, S., van der Kooy, D. (1996). In vivo growth factor expansion of endogenous subependymal neural precursor cell populations in the adult mouse brain. JNeurosci, 16, 2649-58. 

Armstrong, R.J., Tyers, P., Jain, M, Richards, A., Dunnett, S.B., Rosser, A.E., Barker, R.A. (2003). Transplantation of expanded neural precursor cells from the developing pig ventral mesencephalon in a rat model of Parkinson s disease. Exp Brain Res, 151, 204-17. 

FIGURE 5-31 Structure of skeletal muscle, (a) Muscle fibers consist of single, elongated, multinucleated cells that arise from the fusion of many precursor cells. Within the fibers are many myofibrils (only six are shown here for simplicity) surrounded by the membranous sarcoplasmic reticulum. The organization of thick and thin filaments in the myofibril gives it a striated appearance. When muscle contracts, the I bands narrow and the Z disks come closer together, as seen in electron micrographs of (b) relaxed and (c) contracted muscle. 

Several effects of forskolin on B-lymphocytes, the cells of the immune system responsible for the production of immunoglobulins, have further been reported. This diterpene was found to inhibit cellular proliferation of B cells stimulated either by antibodies to surface immunoglobulins (anti-mu), and an antibody to CD20 antigen or 12-O-tetradecanoyl phorbol 13-acetate [219]. There was also a clear inhibition of G1 entry and DNA synthesis, and forskolin maintained its inhibitory effect even when added later after anti-mu stimulation. Additionally, no differences were found in the inhibitory effect of forskolin on neoplastic B cells, as compared to the responses of normal cells. Growth inhibition associated with an accumulation of cells in G1 was later found when cells of the B-lymphoid precursor cell line Reh were incubated with forskolin [220]. In that study, a delay of cells in G2/M prior to G1 arrest was observed, suggesting that important restriction points located in the G1 and G2 phases of the cell cycle may be controlled by forskolin (due to cAMP levels elevation). In a subsequent study [221], it was found that the arrest of Reh cells was accompanied by rapid dephosphorylation of retinoblastoma protein, which was suggested to be a prerequisite for the forskolin mediated arrest of these cells in Gl. 

Fig. 17.8. MS/MS schematic representation of MS/MS by quadrapole mass spectrometers. (A) Sample entry normally via ESI. (B) Precursor ion selection allowing only the ion of interest to continue through the mass spectrometer. (C) Collision-induced dissociation of the ion within a gas cell normally containing argon to produce fragments. (D) The products of fragmentation are focused and analysed via a ToF-mass analyser.

Recently, lamivudine [LAM ih vue deen] or (-)-2 -deoxy-3 -thiacyti-dine (3TC) has been approved for treatment of HIV in combination with zidovudine. This dideoxynucleoside terminates the synthesis of the proviral DNA chain and also inhibits reverse-transcriptase of both HIV and hepatitis B virus (HBV). However, it does not affect mitochondrial DNA synthesis or bone marrow precursor cells. Resistance to zidovudine develops more slowly with the combination. Lamivudine has good bioavailability on oral administration and depends on the kidney for excretion. Though generally well tolerated, pancreatitis develops in a significant number of pediatric... 

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