Developmental expression of Toll‑like receptors in the guinea pig lung

The guinea pig is a useful model for investigating infectious and non-infectious lung diseases due to the sensitivity of its respiratory system and susceptibility to infectious agents. Toll-like receptors (TLRs) are important components of the innate immune response and are critical for lung immune function. In the present study, the differentiation of epithelial cells in the guinea pig lung was examined during gestation by studying anatomic morphology and the major epithelial cell types using cell type-specific markers. The developmental expression of all 9 TLRs and the TLR signaling adaptors myeloid differentiation factor 88 (MyD88) and tumor necrosis factor receptor associated factor 6 (TRAF-6) were investigated by reverse transcription-quantitative polymerase chain reaction and western blotting analysis. The formation of lung lobes in guinea pigs was observed at 45 days of gestation (dGA), along with the expression of the basal cell marker keratin 14 and the alveolar type II cell marker pro-surfactant protein. However, the cube cell marker secretoglobin family1A member 1 and ciliated cell marker b-tubulin IV were only detected in the lungs from 52 dGA onward. The expression levels of all TLRs, MyD88 and TRAF-6 were determined in lung tissues harvested from embryos, newborn, postnatal and adult animals. The expression levels of all TLR signaling components displayed similar dynamic expression patterns with gestation age and postnatal maturation time, except for TLR-4 and TLR-7. mRNA expression levels of TLR components were significantly increased in the lungs at 45 and 52 dGA, compared with later developmental stages. These results suggest that TLR expression in the guinea pig lung is developmentally regulated, enhancing the understanding of lung biology in guinea pig models.