The process of fighting off disease requires that the body mount an appropriate antibody or immune response.

When there is a porcine circovirus type 2 (PCV2) infection in the pig, the result is a depressed antibody response of undetermined cause.
To learn more, a comparative study was conducted using 64 isolated, germ-free piglets infected with one of three respiratory pathogens – PCV2, porcine reproductive and respiratory syndrome (PRRS) virus or swine influenza virus (SIV).

Preliminary results indicated that germ-free piglets could clear SIV within 21 days, while piglets infected with PCV2 and PRRS virus were unable to do so.

The trial clearly revealed that neither PRRS virus-infected piglets nor PCV2-infected piglets activated cytotoxic or helper T cells at the site of infection. The cytotoxic cells destroy virus-infected cells, while the helper T cells stimulate the production of antibodies.

PCV2 infections showed depressed development of helper T cells and thus support suggestions of immune suppression related to this disease. But the cause of the depressed antibody response could not be determined.

Since piglets infected with PCV2 were unable to develop a mature immune system or to mount robust antibody responses, researchers hypothesize that PCV2 vaccines in the future should be polyvalent, meaning that they would include bacterial adjuvants, such as probiotics, to simultaneously stimulate the development of cytotoxic T cells and activated helper T cells.

PRRS virus infection causes the depletion of B cells that could potentially respond to the virus. PRRS virus vaccine development should focus on recombinant and modified vaccines that reduce the loss of B cells while still promoting an immune response.

The germ-free pig model can serve as an important test vehicle for the future development of vaccines for PCV2.

Funding for this research was provided by the National Pork Board.

Researcher: John Butler, University of Iowa. For more information, contact Butler at john-butler@uiowa.edu.