Richard R. Schmidt

Altered Development of Immunocompetence Following Prenatal or Combined Prenatal-Postnatal Insult: A Timely Review

There is an unequal distribution of interest between assessment of immunocompetence at the adult level following the administration of various agents/protocols and evaluation of immunocompetence postnatally subsequent to prenatal insult. This paper reviews the effects of dietary manipulation, selected pharmaceuticals, and certain environmental agents on the functional status of the postnatal immune system after in utero exposure to these agents and protocols. These data are discussed in light of what has also been observed for adult exposure to the same or similar experimental design. A discussion of congenital disorders of immunocompetence is also provided. Alteration in the development of postnatal immunocompetence following prenatal insult may manifest itself in several ways, some of which may reflect a permanent defect while others may be of a transient nature. In either instance, however, it behooves scientists in all arenas to (1) determine the precise nature and magnitude of such developmentally related immunologic deficits and (2) focus on the selection and standardization of the most relevant procedures to be employed in the assessment of immunocompetence.

Differential eicosanoid synthesis by murine fetal thymic non-lymphoid cells

The temporal patterns of synthesis of prostaglandin (PG)E2 and PGI2 by organ‐cultured fetal thymic lobes and the cell population(s) responsible for synthesis of such products within the murine fetal thymus have been investigated. Embryonic day 14 thymic lobes were organ‐cultured in defined media for 14 days and the media were collected every 24 h and replaced with fresh media. Collected media were processed for quantitation of either PGE2 or PGI2. Lobes were also cultured in 2′‐deoxyguanosine (1.35 mmol/L) to produce an enriched non‐lymphoid population. The per cent cyclooxygenase‐positive cells within non‐lymphoid cell‐enriched lobes as well as the capacity of such lobes to synthesize either PGE2 or PGI2 were determined and compared with that of intact thymic lobes. Results demonstrate that fetal thymic lobes, in vitro, differentially synthesize PGI2 and synthesize PGE2 at a constant rate. Moreover, lobes enriched for non‐lymphoid cells contain a greater percentage of cyclooxygenase‐positive cells and synthesize increased amounts of eicosanoids per 104 cells compared with controls.

9-methyl pteroylglutamic acid, a synthetic analogue of folic acid: its effects on hexosamine levels in fetal rat limbs and other fetal tissues.

Pregnant rats were administered the teratogen and synthetic analogue of folic acid, 9-methyl pteroylglutamic acid, on the 11th day of gestation and placed on a semisynthetic diet containing the antagonist but lacking the vitamin until the 14th gestational day. This transitory maternal folic acid deficiency results in multiple congenital skeletal malformations. Control animals were administered a folic acid-supplemented regimen. Hexosamine levels were measured in fetal tissues, i.e. limbs, livers, and yolk sacs, in order to monitor the accumulation of a primary constituent of the extracellular matrix, i.e. glycosaminoglycans. Fetal tissues were obtained for hexosamine analysis on the 16th and 18th days of gestation. The teratogenic and transitory folic acid-deficient regimen resulted in (1) a significant reduction in the accumulation of hexosamine in fetal limbs by the 16th day of gestation, and (2) a significant increase in the accumulation of hexosamine in fetal livers by the 16th day of gestation. The regimen was observed to have had no effect on hexosamine accumulation by the yolk sac. Furthermore, no significant effect on hexosamine accumulation from the 16th to the 18th day of gestation was observed in any of the tissues studied.

Rapid isolation of intact, viable fetal cartilage models

A rapid procedure is described for the isolation of viable, intact, femoral cartilage models (humeri and femora) obtained from pregnant rats on the 18th day of gestation. Viability of these models is demonstrated in an in vitro system where the incorporation of 35S-sulfate was linear with time of incubation and with numbers of cartilage models utilized. Treatment of cartilage models with ice-cold trichloroacetic acid and a boiling water bath prior to incubation with radiolabel, reduced the amount of radioactivity incorporated to 1.3% of that observed for models incubated by routine procedures. Furthermore, digestion of cartilage model homogenates with protease yielded a supernatant from which 51% to 57% of the radioactivity was precipitated as GAG. This method may also be used to isolate fetal cartilage models as early as the 16th day of gestation. with this system, specific biochemical parameters of mammalian fetal chondrogenesis may be surveyed in normally and abnormally developing fetal cartilage free of surrounding soft tissue.

Effect of a Synthetic Folic Acid Analogue, 9-Methyl-Pteroylglutamic Acid, on Fetal Chondrogenesis: Ultrastructural Observations

Maternally administered folic acid antagonists (x-methyl-PGA and 9-methyl-PGA) are known to produce various skeletal malformations in the neonate. These defects are thought to be due in part to abnormal metabolism and/or deposition of various extracellular matrix components, i.e., collagen and glycosaminoglycans. Experimental reduction of glycosaminoglycan biosynthesis in vitro has been shown previously to alter the spatial orientation and normal pattern of collagen fibrillogenesis. Furthermore, dietary withdrawal of folic acid concomitant with maternal administration of 9-methyl-PGA has been shown to result in abnormal collagen, uronic acid, and hexosamine metabolism by fetal limbs. In the present study pregnant rats were exposed to a transitory folic acid deficiency from day 11 to 14 of gestation and fetal tibias (mid-diaphyseal region) were examined with the electron microscope on day 18 of gestation. Although we were unable to ascertain any aberrant patterns of fibrillogenesis and orientation with respect to collagen, this particular teratogenic regimen resulted in an altered pattern of chondrocyte development when observed at the ultrastructural level.