Immunobiology of chicken germinal center: II. Accumulation of apoptotic cells within the germinal center.

The germinal center (GC) develops after antigen stimulation and is thought to occur at the site of various immune responses. We observed apoptotic cells within the GC using in situ end labeling (TUNEL), small amount DNA ladder assay, and RT-PCR analysis of Bcl-2 mRNA expression. Apoptosis was detected within GCs at all phases of the GC reaction by both TUNEL and DNA ladder assays. The number of TUNEL(+) nuclei within the GC did not increase over the course of the GC reaction. However, the density of DNA in the ladder assay was higher in later-phase GCs. Bcl-2 mRNA expression was detected within GCs during the early phases of the GC reaction. These results indicate that accumulation of apoptotic cells and rescue from apoptosis occur within chicken GCs. In the present paper, the reasons for the accumulation of apoptotic cells will be discussed.