Comparative effects of vaccination against porcine circovirus type 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV) in a PCV2-PRRSV challenge model

Abstract

The objective of the present study was to determine the effects of porcine circovirus type 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV) vaccinations in an experimental PCV2-PRRSV challenge model, based on virological (viremia), immunological (neutralizing antibodies [NAs], gamma interferon-secreting cells [IFN-γ-SCs], and CD4(+) CD8(+) double-positive cells), and pathological (lesions and antigens in lymph nodes and lungs) evaluations. A total of 72 pigs were randomly divided into 9 groups (8 pigs per group): 5 vaccinated and challenged groups, 3 nonvaccinated and challenged groups, and a negative-control group. Vaccination against PCV2 induced immunological responses (NAs and PCV2-specific IFN-γ-SCs) and reduced PCV2 viremia, PCV2-induced lesions, and PCV2 antigens in the dually infected pigs. However, vaccination against PCV2 did not affect the PRRSV immunological responses (NAs and PRRSV-specific IFN-γ-SCs), PRRSV viremia, PRRSV-induced lesions, or PRRSV antigens in the dually infected pigs. Vaccination against PRRSV did not induce immunological responses (PRRSV-specific IFN-γ-SCs) or reduce PRRSV viremia, PRRSV-induced lesions, or PRRSV antigens in the dually infected pigs. In addition, vaccination against PRRSV increased PCV2 viremia, PCV2-induced lesions, and PCV2 antigens in the dually infected pigs. In summary, vaccination against PCV2 reduced PCV2 viremia, PCV2-induced lesions, and PCV2 antigens in the dually infected pigs. However, vaccination against PRRSV increased PCV2 viremia, PCV2-induced lesions, and PCV2 antigens in the dually infected pigs. Therefore, the PCV2 vaccine decreased the potentiation of PCV2-induced lesions by PRRSV in dually infected pigs. In contrast, the PRRSV vaccine alone did not decrease the potentiation of PCV2-induced lesions by PRRSV in dually infected pigs.

Fig 1

(A) Mean serum NA titers against PCV2. (B) Mean genomic copy numbers of PCV2 DNA in serum samples. (C) Mean numbers of PCV2-specific IFN-γ-SCs in PBMCs. ■, pigs which received the PCV2 vaccine followed by PCV2 challenge only (group 1); □, pigs which received the PCV2 vaccine followed by dual challenge (group 2); ♢, pigs which received the PRRSV vaccine followed by dual challenge (group 4); ○, pigs which received both the PCV2 and PRRSV vaccines followed by dual challenge (group 5); ▲, pigs which were challenged with PCV2 (group 6); ●, pigs which were challenged with PCV2 and PRRSV (group 8). Different letters (a, b, and c) indicate significant (P < 0.05) differences between groups.

Fig 2

(A) Mean anti-PRRSV IgG antibody levels in serum samples. (B) Mean genomic copy numbers of PRRSV DNA in serum samples. (C) Mean numbers of PRRSV-specific IFN-γ-SCs in PBMCs. □, pigs which received the PCV2 vaccine followed by dual challenge (group 2); ◆, pigs which received the PRRSV vaccine followed by PRRSV challenge (group 3); ♢, pigs which received the PRRSV vaccine followed by dual challenge (group 4); ○, pigs which received both the PCV2 and PRRSV vaccines followed by dual challenge (group 5); △, pigs which were challenged with PRRSV (group 7); ●, pigs which were challenged with PCV2 and PRRSV (group 8). Different letters (a, b, and c) indicate significant (P < 0.05) differences between groups. S/P, sample to positive ratio of ≥0.4 is considered to be positive.

Fig 3

Analyses of CD4⁺ CD8⁺ double-positive cells (A) and CD4⁺ cells (B) in PBMCs from the different groups. From left to right, the bars indicate the following groups: pigs which received the PCV2 vaccine followed by PCV2 challenge only (group 1), pigs which received the PCV2 vaccine followed by dual challenge (group 2), pigs which received the PRRSV vaccine followed by PRRSV challenge (group 3), pigs which received the PRRSV vaccine followed by dual challenge (group 4), pigs which received both the PCV2 and PRRSV vaccines followed by dual challenge (group 5), pigs which were challenged with PCV2 (group 6), pigs which were challenged with PRRSV (group 7), pigs which were challenged with PCV2 and PRRSV (group 8), and negative-control pigs (group 9). Different letters (a, b, and c) indicate significant (P < 0.05) differences between groups.

Fig 4

Immunohistochemistry for detection of PCV2 antigens in lymph nodes. (A) PCV2 antigens (arrows) were detected at 21 dpc in granulomatous inflammations of lymph nodes from pigs which received the PRRSV vaccine followed by dual challenge (group 4). (B) PCV2 antigens (arrow) were occasionally detected at 21 dpc in macrophages of lymph nodes from pigs which were challenged with PCV2 (group 6).

Fig 5

Immunohistochemistry for detection of PRRSV antigens in the lung. (A) PRRSV antigens (arrows) were detected at 21 dpc in macrophages in severely thickened alveolar septa of lungs from pigs which received the PRRSV vaccine followed by dual challenge (group 4). (B) PRRSV antigens (arrow) were occasionally detected at 21 dpc in macrophages in mildly thickened alveolar septa of lungs from pigs which received the PRRSV vaccine followed by PRRSV challenge (group 3).