Presence of paf-acether in human thymus

PAF and Haematopoiesis. I. 5-Fluoro-Uracil Induces PAF Production in Haematopoietic Organs of Rats

Haematopoietic organs of rats were examined for the presence of platelet-activating factor (PAF) and acetylhydrolase before and after treatment with 5-fluoro-uracil (5-FU) (200 mg/kg) a chemotherapeutic compound with apoptotic effects. PAF was reported in thymus, spleen and femoral bone marrow of rats with or without 5-FU. Although acetylhydrolase activity in organs was not affected by 5-FU treatment, elevated levels of PAF were observed in thymus and spleen. For the first time PAF is reported in haematopoietic organs of rats, strengthening in vitro data suggesting its role in the apoptotic processes in thymus, in the modulation of the immune response, and in the regulation of haematopoiesis.

PAF and haematopoiesis: III. Presence and metabolism of platelet-activating factor in human bone marrow

Platelet-activating factor (PAF) is a phospholipid compound with major immunoregulatory activities. The present study shows that human bone marrow contains 576 +/- 39 pg PAF/ml (n = 35). Bone marrow-derived PAF exhibits the same biophysical and biological properties that synthetic PAF. PAF concentrations in bone marrow are correlated with the granulocyte (r = 0.4, P = 0.02) but not with the lymphocyte (r = 0.24, P = 0.17) and the monocyte (r = 0.12, P = 0.48) counts. In bone marrow PAF is inactivated by a plasma PAF acetylhydrolase activity (48.0 +/- 2.3 nmol/min per ml, n = 34). Experiments with [3H]PAF indicate that human bone marrow cells actively metabolize this potent molecule by the deacetylation-transacylation pathway. Results of this investigation indicate the permanent presence of significant amounts of PAF in bone marrow suggesting its putative involvement in the processes of bone marrow cell proliferation and maturation.

PAF and haematopoiesis. IV. Modifications of spleen and thymus PAF contents after a single dose of the chemotherapeutic drug 5-fluorouracil in mice

The spleen and thymus of mice were examined for the presence of PAF after injection of 5-fluorouracil (5-FU) (200 mg/kg). A significant increase of the spleen (P = 0.005) and thymus (P < 0.05) PAF concentrations was noted 48 h after 5-FU infusion. PAF levels in thymus are similar to those of controls from days 4 to 14. By contrast, spleen PAF significantly decreased (0.005 < P < 0.03) from days 7 to 14. Conversely, the 5-FU administration did not modify the spleen and plasma acetylhydrolase activity, suggesting that the variations of PAF levels in thymus and spleen were mainly due to differences of local PAF production. Thus, the chemotherapeutic drug 5-FU modulates in vivo PAF production in haematopoietic organs of mice. Considering the effects of PAF in the processes of B- and T-cell proliferation and functions, these results could be of importance for the role of PAF during human cancer therapy and haematopoiesis in vivo.

Quantitation of IL-4 expression in small numbers of cells from mice

Interleukin-4 (IL-4) is an important T cell and mast cell product that participates in allergic and cytotoxic responses, as well as functions as a growth factor for B, T, and inflammatory cells. Studies of the expression of IL-4 by T cells present in inflammatory reactions would be facilitated by using polymerase chain reaction (PCR) coupled to reverse transcription of mRNA to amplify the small quantity of mRNA present in these cells. In order to use this method in a quantitative manner, a plasmid was constructed that contained a modified form of mouse IL-4 cDNA. This plasmid was transcribed to produce cRNA for this modified sequence. The cRNA was used as an internal standard for the reverse transcription and amplification of IL-4 transcripts in RNA samples from mouse thymocytes. Amplification of reverse-transcribed native IL-4 mRNA produced a 286 bp PCR product. Amplification of the reverse-transcribed standard RNA produced a 155 bp product, which reflected a deletion introduced into the original IL-4 cDNA sequence. Comparison of the amount of the 286 bp native product to the amount of 155 bp standard product enabled the quantitative determination of IL-4 expression in each sample. This method was used to demonstrate that platelet activating factor increases the expression of IL-4 in mouse thymocytes and in a mouse T cell line. The expression of IL-4 by thymocytes exposed to platelet-activating factor (PAF) may reveal an important link between inflammation and the maturation of T cells in the thymus.

Induction of high-affinity paf receptor expression during T cell activation

Activated human T cells via the CD2 or the CD3 pathways exhibited a higher capacity than resting T lymphocytes to incorporate and metabolize [3H]pafacether (paf) at 37 degrees C. Resting T lymphocytes lacked specific binding capacity for paf, yet high-affinity paf receptors (paf-R) were induced on CD3- or CD2-dependent activation. This up-regulation in the number of paf-R became apparent by day 1 of culture, reached a maximum of about 25,000 sites cell by days 4 to 6 and subsequently declined. Interestingly, human recombinant interleukin-2 in a dose-dependent manner prevented the decrease of high-affinity paf-R expression on T cells. By contrast, the receptor affinity was constant throughout the culture period. Thus, paf-R at different stages of T cell activation were indistinguishable with respect to receptor-ligand interaction, and differed only in their number. Together, these data demonstrate that after activation human T cells develop membrane high-affinity paf-binding sites. They also suggest for the first time that expression of the paf-R are coupled to T cell activation and/or differentiation.