Abstract: Abstract: Nine 32-day-old conventional piglets free of infection with PCV-2 were used, distributed in three groups: control（n=3）， pigs inoculated with PCV-2 alone（PCV-2，n=3），PCV-2 inoculated and KLH immunostimulated（PCV-2+ KLH ，n=3）. From all pigs , superficial inguinal lymph nodes were collected for histological examination after 32 days postinoculation, immunohistochemistry for PCV-2 detection. Location of apoptotic cells was detected with TUNEL and cell cycle and apoptotic rate were measured by flow cytomtry . The results indicated that characteristic histopathological lesions of the lymph nodes in PCV-2 and PCV-2+KLH were lymphocyte depletion in cortex and paracortex , epithelioid-like macrophages infiltration, intracytoplasmic inclusion bodies presented in epithelioid –like macrophages. PCV-2 was mainly found in epithelioid –like macrophages by immunohistochemistry. In the lymph nodes, lymphocytes presented higher rates of apoptosis in the cortex by TUNEL, special B-cell areas, similar apoptotic cells were found in this compartment in control. Apoptotic rates of lymph nodes were 0.41%, 3.34% and 4.88% in control, PCV-2 and PCV-2 + KLH by flow cytometry , respectively. The apoptotic rates of lymph nodes for PCV-2 and PCV-2 + KLH pigs were significantly higher than those for control group (P < 0.05 and P < 0.01). Proliferation index(PI) was 0.17±0.01、0.12±0.01和0.12±0.04 in control, PCV-2 and PCV-2 + KLH group, the date of control group was higher than the other group, but without statistical difference. It is concluded that PCV-2 can induce lymphocyte depletion in lymph nodes of piglets by blocking cells proliferation and promoting apoptosis . This is one of the mechanism of immunosuppression on infected piglets by PCV-2.

Key words: Apoptosis, Virus Located, Lymph node, PCV-2, Piglets