Developmental immunotoxicology assessment in the rat: Age, gender, and strain comparisons after exposure to lead

A delayed-type hypersensitivity response (DTH) measured against keyhole limpet hemocyanin (KLH) and an enzyme-linked immunosorbant assay (ELISA) for anti-KLH IgG antibody were studied for potential use as biomarkers for the assessment of immunotoxicity after exposure to a xenobiotic during fetal development. Age, gender, site of antigenic challenge, and strain of rat were used as variables. The heavy metal lead was used because it is a known developmental immunotoxin. In the age comparison, untreated juvenile (5-week-old) Sprague-Dawley (CD) rats produced lower levels of antibody and showed a smaller DTH response than adults; only adult males had a statistically significant increase in the DTH response. Both male and female adults showed a statistically significant increase in levels of antibody over those of both genders of weanlings. As to site of KLH challenge, the DTH response was greater in untreated young animals when they were challenged in the footpad rather than the earlobe. Gender differences in antibody levels were evident: females had optimal antibody levels when challenged in the earlobe, whereas males had optimal levels when challenged in the footpad. In a comparison between strains of weanling rats exposed in utero to control acetate or lead acetate (250 ppm lead acetate in drinking water) and examined at 5 weeks of age, the KLH immunization protocol produced a higher antibody response in CD than in F344 rats; in contrast, F344 rats exhibited an elevated DTH response. Exposure to lead in utero via the pregnant dams produced differential gender effects in the juveniles of both strains. Females had a statistically significant decrease in the lead-induced DTH response (p < .05), whereas males did not. This gender effect persisted into adulthood when it was measured in the F344 strain. These results suggest that the DTH and anti-KLH IgG ELISA assays, respectively, are suitable as biomarker assays for the assessment of immunotoxicity after in utero exposure to a xenobiotic; based on the lead exposure results, persistent immunotoxicity can be detected in juvenile as well as in adult rats after fetal exposure that occurred through the dam and after early postnatal exposure that occurred via lactation. Furthermore, these studies provide evidence that there are differential gender effects after in utero exposure to lead that can be detected in juveniles and that also persist into adulthood. Additionally, at the KLH concentration utilized, the balance of cell-mediated versus humoral responses differed between the two strains examined. (Animal protocols complied with National Institutes of Health guidelines and were approved by the Cornell University Institutional Animal Care and Use Committee.).