The aim of study was to investigate porcine circovirus-2 (PCV2) impact on the morphological sight of pig lymph nodes. The research was carried out in 2010. Three Latvian farms were investigated (from Latgale and Kurzeme) and thirty 5-15 weeks old pigs with clinical signs of Postweanig Multisystemic Wasting Syndrome were selected and observed. Four lymph nodes from each animal for histological and immunohistochemical investigations were taken. Thirty structural parameters of a lymph node were detected on histological slides: visualization of follicle structure, lymphocyte depletion and amount of histiocytic cell infiltration. As a result, changes in lymph nodes with PCV2 antigen were detected in all these structural parameters: increasing amount of PCV2 antigen in pig lymph nodes, but the greatest changes were in the follicles structure in lymph node. The increased amount of PCV2 antigen in lymph node; significantly decreases the amount of lymphocytes and increases the amount of histiocytes in them. Porcine circoviruss-2 in lymph node basically distributes from the lymph node cortex into the medulla, as well the amount of PCV2 antigen in lymph node also increased.

High economic losses in agriculture can be caused by pig disease like Postweaning Multisystemic Wasting Syndrome (PMWS). Porcine circovirus-2 (PCV2) is the primary agent of PMWS. It is known that PMWS causes cellular and humoral immunity disorders, therefore it is considered a general immune deficiency disease in piglets. It is still unknown, why piglets with PMWS have severe loss of lymphocytes in lymphoid tissues and in the blood. Thus, the hypothesis of the study was that lymphocyte depletion occurs because of lymphocyte life-cycle delay in pigs infected by PCV2. The activity of cell life-cycle is attributed to protein Ki67. This protein is found in all active phases of the cell like interphase G1, S, G2 and mitoses. However, protein Ki67 is not observed at all in the cell’s “quiet” phase G0. The aim of our work was to investigate the lymph node cell proliferation activity of pigs infected by PCV2. In total, 42 pig carcasses were collected from 5 to 15 weeks old pigs with PMWS clinical manifestation. Lymph nodes were selected from each pig carcass for histological and immunohistochemical testing. We concluded that B lymphocyte population was reduced first in the lymph node with PCV2, but the number of T lymphocytes decreased later. PCV2 decreased B lymphocyte proliferation activity.