Do white cells matter in white matter damage?

Support is provided for the hypothesis that activated leukocytes, especially monocytes/macrophages, contribute to cerebral white matter damage in extremely low gestational age newborns. Much of the evidence is indirect and comes from analogies to brain diseases in adults, and from models of brain damage in adult and newborn animals. If the recruitment of circulating cells to the brain contributes to white matter damage in extremely low gestational age newborns, then minimizing the transendothelial migration of circulating cells by pharmacological manipulation might prevent or reduce the occurrence of neonatal white matter damage and the disabilities that follow.

Gastrointestinal cells of IL-7 receptor null mice exhibit increased sensitivity to irradiation

IL-7 is a critical cytokine in the development of T and B cells but little is known about its activity on nonhematopoietic cells. An unexpected finding was noted in allogeneic bone marrow transplant studies using IL-7 receptor null (IL-7R alpha(-/-)) mice as recipients. These mice exhibited a significantly greater weight loss after total body irradiation compared with wild type, IL-7R alpha(+/+), mice. Pathological assessment indicated greater intestinal crypt damage in IL-7R alpha(-/-) recipients, suggesting these mice may be predisposed to gut destruction. Therefore, we determined the effect of the conditioning itself on the intestinal tract of these mice. IL-7R alpha(-/-) mice and IL-7R alpha(+/+) mice were irradiated and examined for lesions and apoptosis within the small intestine. In moribund animals, IL-7R alpha(-/-) mice had extensive damage in the small intestine, including marked ablation of the crypts and extreme shortening of villi following 1500 cGy total body irradiation. In contrast, by 8 days after irradiation, the small intestines of IL-7R alpha(+/+) mice had regenerated as distinguished by normal villus length and hyperplastic crypts. Following 750 cGy irradiation, IL-7R alpha(-/-) mice had a higher proportion of apoptotic cells in the crypts and an accompanying increase in the pro-apoptotic protein Bak was expressed in intestinal epithelial cells. These results demonstrate the increased radiosensitivity of intestinal stem cells within the crypts in IL-7R alpha(-/-) mice and a role for IL-7 in the protection of radiation-induced apoptosis in these same cells. This study describes a novel role of IL-7 in nonhematopoietic tissues.

IL-1 mRNA expression detected by in situ hybridization and polymerase chain reaction in human thymus and thymoma. Correlation with late T-cell maturation in normal versus neoplastic thymus

Interleukin-1 has long been suggested to participate in the development of T-cells in the thymus. To determine whether IL-1 was produced in the human thymus, we used the technique of in situ hybridization and PCR amplification of mRNA. High levels of IL-1 mRNA were detected in cells at the cortico-medullary border, which separates immature from mature T-cells, suggesting a role for IL-1 in a late stage in T-cell maturation. IL-1 transcripts were detectable by a single step PCR reaction in these samples. We examined a series thymomas (human thymic epithelial tumors) that induce partial T-cell maturation: In this group of thymomas T-cells develop to the cortical stage but not beyond. We failed to detect high levels of IL-1 mRNA expression in these tumors by in-situ hybridization, IL-1 mRNA was detected only in one of these samples by a single step PCR amplification. However, all of the samples were positive, when analyzed with a more sensitive, two step amplification of IL-1 mRNA by the use of nested primers. These results are consistent with the hypothesis that higher level of IL-1 expression is either the consequence of, or required for late T-cell maturation.

Interleukin-1 stimulates prostaglandin biosynthesis by human amnion

The purpose of these studies was to determine if Interleukin-1 (IL-1) alters the rate of prostaglandin biosynthesis by human amnion. Primary monolayer cultures of amnion cells were established from women undergoing elective cesarean section before the onset of labor. Natural purified and recombinant human IL-1 alpha and IL-1 beta were incubated with amnion cells in culture, and prostaglandin E2 (PGE2) biosynthesis was measured by radioimmunoassay in cell-free media. A concentration-dependent increase in PGE2 production by amnion cells occurred in response to natural purified and recombinant IL-1 preparations. No differences in the parameters of the dose-response curves between the two IL-1 gene products could be determined (p greater than 0.05). Indomethacin blocked the effect of IL-1 in prostaglandin biosynthesis by human amnion. Interleukin-1, a fever mediator, could serve as a signal for the initiation of labor in cases of intrauterine or systemic infection.

Specific inhibition of lymphokine biosynthesis and autocrine growth using antisense oligonucleotides in Th1 and Th2 helper T cell clones

T helper cells have recently been divided into two subsets. The Th1 subset secretes and responds to IL-2 in an autocrine manner. The Th2 subset upon mitogen or antigen stimulation releases IL-4. Here we describe a novel technology that allowed us to confirm this distinction. We have used synthetic oligonucleotides complementary to the 5' end of mouse IL-2 and IL-4 to specifically block the biosynthesis of IL-2 or IL-4 in two murine helper T cell clones from the Th1 or Th2 subset. We show that the antisense IL-2 oligonucleotide inhibited the proliferation of the Th1 clone and had no effect on the Th2 clone. In parallel experiments, the antisense IL-4 oligonucleotide blocked the proliferation of the Th2 clone and not the proliferation of the Th1 clone. The inhibition was significantly reversed in both cases by the addition of the relevant lymphokine (IL-2 in the case of the Th1 clone, IL-4 in the case of the Th2 clone). Northern analysis, using cDNA probes specific for the two lymphokines, showed a decrease in the steady-state level of the relevant lymphokine mRNA, suggesting the specific degradation of the mRNA by an RNase H-like enzymatic activity. This strategy, which allows the specific blockade of the biosynthesis of a lymphokine, could be useful for future studies on the role of each T helper subset in physiological immune responses.

Do blood and meconium affect the detection of endotoxin in amniotic fluid with the limulus amebocyte gel clot assay?

The limulus amebocyte lysate (LAL), assay is the most sensitive technique for the detection of endotoxin in biological fluids. Because endotoxin is a component of gram-negative bacteria, the assay has been employed in the detection of gram-negative bacterial contamination of biological fluids. The LAL assay is rapid, inexpensive, easy to perform, and requires little laboratory expertise. When used in conjunction with the gram stain examination of amniotic fluid, it improves the detection of intra-amniotic infection before the availability of culture results. However, the usefulness of the LAL assay in the detection of endotoxin in other body fluids is limited by the presence of an inhibitor to the gelation of the assay. The studies reported in this communication were undertaken to establish if amniotic fluid contains such an inhibitor. Sterile amniotic fluid (AF) samples obtained from 93 patients by transabdominal amniocentesis before labor were used to determine the ED 50 dose of endotoxin necessary for a positive LAL result. The ED 50 dose of endotoxin required for gelation was significantly higher when AF--rather than pyrogen-free saline--was used as the diluent, implying that inhibitors are in fact present (ED 50 = 58.3 pgm/ml). The presence of blood or meconium in the AF did not enhance inhibition significantly: ED 50 doses were 58.3 pgm/ml and 56.2 pgm/ml, respectively. This is not significantly different from the ED 50 of clear amniotic fluid.

Failure of endotoxin to cross the chorioamniotic membranes in vitro

We have previously reported the detection of endotoxin in the amniotic fluid of patients with gram-negative intra-amniotic infection. Endotoxin or lipopolysaccharide (LPS) is a potent biologic product capable of inducing prostaglandin release from several cell types, and therefore may be involved in the onset of human parturition in the setting of intra-amniotic infection. The experiments outlined in this report were designed to determine whether endotoxin crosses chorioamniotic membranes in vitro. Chorioamniotic membranes obtained at the time of elective cesarean section were placed in Ussing chambers used for transport experiments. Endotoxin was placed in one chamber, and serial timed samples were taken from both chambers for endotoxin quantification, which was performed with the limulus amebocyte gel clot assay. Blue dextran was used to exclude the presence of large defects. Bromophenol blue was used to demonstrate membrane permeability to low-molecular weight substances. Endotoxin failed to cross the chorioamniotic membranes in all experiments (n = 11).

Contrasuppression. A novel immunoregulatory activity

We have described an interaction between two T cells subsets that results in interference with the expression of Ly-1-, 2+ (Ly-2) T cell-mediated suppression. We refer to this novel immunoregulatory activity as contrasuppression. The T cell responsible for the induction of contrasuppression (inducer cell) expresses the phenotype Ly-1-, 2+;I-J+;Qa-1+. This phenotype distinguishes it from the suppressor effector cells which we find to be I-J-2.3. An I-J+ soluble mediator from the contrasuppressor inducer cell acts on another cell (acceptor cell) that expresses the phenotype Ly-1+, 2+; I-J+; Qa-1+. This phenotype distinguishes it from T helper cells. Both the inducer cell (or its biologically active mediator) and its acceptor cell are required for the expression of contrasuppression. Because contrasuppressor cells can block the suppressive activity of cell-free mediators released by Ly-2 suppressor T cells, the mechanism of contrasuppression is either separated from or in addition to the inactivation of suppressor cells themselves. The potential importance of contrasuppressor activity in the regulation of suppressor T cell activity in allowing immunologic memory to be expressed and in permitting microenvironmental immune regulation is discussed.