In vitro responses of avian monocytes to homologous yolk

Large volumes of yolk are released into stromal lacunae of the avian ovary during bursting atresia. It is broken down by macrophages that accumulate in large numbers in the lacunae in the presence of free yolk. The macrophages may be derived from lacunae-lining cells or from blood monocytes.

Chicken blood monocytes were isolated from adult laying hens, cultured, and exposed to different concentrations of homologous yolk. Morphological changes were studies by light microscopy and transmission and scanning electron microscopy, and the rate of breakdown of yolk micelles was measured by turbidometry. Tritiated thymidine uptake was used to measure monocyte proliferation rate following exposure to yolk.

Following exposure to yolk, the cells rapidly changed from fibroblastlike to macrophagelike cells. The turbidometric results indicated very significant clearing of yolk micelles by the cultured monocytes. These findings were supported by light and transmission and scanning electron microscopy, which showed these cells to be extremely active in engulfing yolk particles.

This process in cultured monocytes is morphologically identical to that observed in previous studies in cells lining the lacunae of ovaries of hens, in which large yolky follicles are undergoing bursting atresia. Therefore, it should serve as a model for studying yolk resorption during this form of atresia.