Cyclosporine effect on anti-CD3 monoclonal antibody-stimulated mitogenesis, phorbol ester comitogenesis, and PGE2 production

Human peripheral blood mononuclear cells (H-PBMC) from 10 healthy donors were stimulated to proliferate with phytohemagglutinin lectin (PHA), anti-CD3 monoclonal antibody (mAb), and anti-CD3 mAb plus phorbol 12, myristate 13 acetate (TPA), a protein kinase C (PKC) agonist. Anti-CD3 mAb-mediated mitogenesis was 35-75% of that observed with PHA. When TPA was added to a dose of mAb that by itself did not cause mitogenesis, proliferation equal to 50-90% of the maximally mitogenic dose occurred. TPA did not enhance proliferation with maximally mitogenic doses of antibody. Dimethyl-prostaglandin E2, dibutyryl cyclic AMP, and forskolin (an adenyl cyclase agonist) inhibited PHA, anti-CD3, and anti-CD3/PMA-mediated mitogenesis. Cyclosporine (CSA) inhibited anti-CD3 and anti-CD3/TPA mitogenesis in a dose-dependent fashion. While CSA inhibited anti-CD3 and anti-CD3/TPA mitogenic signals, it did not affect PGE2 production by anti-CD3 mAb-stimulated H-PBMC. In the presence of CSA, PGE2 production in PHA-stimulated H-PBMC was increased. PGE2 inhibits lymphocyte proliferation via a cyclic AMP-mediated mechanism and may enhance maturation of suppressor cells. CSA inhibits anti-CD3 mAb and anti-CD3/TPA proliferative signals in H-PBMC yet has no effect or may even enhance production of suppressive PGE2. The maturation of antigen-specific suppressor cells elicited by CSA may involve active down-regulation of CD3 receptor and PKC-dependent events while PGE2 production continues.     

CT of the normal pituitary stalk

A prospective study assessed the size and frequency of visualization of the normal pituitary stalk on high-resolution computed tomography (CT). The normal pituitary stalk can be seen on the vast majority of high-resolution scans obtained with thin sections and intravenous contrast material. The upper size limit of the normal pituitary stalk is 4 mm at the level of the dorsum sellae and 4.5 mm above the dorsum. Stalks larger than this should be viewed with suspicion. Comparison of the size of the pituitary stalk with that of the nearby basilar artery is possible on most CT scans, providing a convenient and reliable visual check of the size of the stalk.     

Pulmonary atelectasis: signal patterns with MR imaging

To assess the signal characteristics of different types of pulmonary atelectasis on magnetic resonance (MR) images, the authors studied obstructive atelectasis (OA) in 17 patients and nonobstructive atelectasis (NOA) in 25 patients. All patients underwent electrocardiographically gated MR imaging studies of the thorax with standard spin-echo sequences. No signal differences were observed between either type of atelectasis on T1-weighted images. Conversely, OA and NOA appeared significantly different on spin-density-weighted images (P less than .001) and on T2-weighted studies (P less than .0001). On T2-weighted images, all 17 cases of OA appeared hyperintense, whereas 22 of 25 cases of NOA demonstrated a very low signal intensity. Differences in the pathophysiology of OA and NOA presumably account for this observation. In OA, alveolar air is totally resorbed and secretions accumulate in the obstructed lung. The resulting increase in free fluid prolongs the T2 relaxation times and leads to high signal intensity on T2-weighted images. In NOA, the short T2 relaxation time of lung tissue in the absence of secretions and potential magnetic susceptibility effects due to residual air are likely to be responsible for the low T2 signal pattern.