Immune responses of specific pathogen free foals to EHV-1 infection.

This research article examines the immune responses of foals, raised under specific pathogen free (SPF) conditions, to equine herpes virus type 1 (EHV-1) infection. The study found that the virus induced symptoms that recovered within seven days, but stayed detectable in nasal mucus for at least 10 days. The SPF foals’ immune systems responded by producing interferon, antibodies, and other immune responses.

Experiment Design and Findings

• Four foals were raised under SPF conditions and another non-SPF foal were inoculated with EHV-1 when they were 3 to 4 months old. This was to investigate their immune responses when exposed to a specific pathogen like EHV-1.
• Post-infection, the foals exhibited clinical signs such as depression, fever, inappetence, and coughing, which completed recovery in seven days. However, the virus remained detectable in the nasal mucus for at least 10 days after inoculation, indicating that though clinical signs had resolved, the virus was still present in their bodies.
• The clinical illness was less severe in the non-SPF foal, implying that exposure to various pathogens prior to the study may have fortified the foal’s immune system.

Immune Responses to EHV-1 Infection

• Interferon, a protein that the immune system produces in response to viral infections, was detected in all the foals from 2 days post infection (dpi), demonstrating an immediate response to the virus.
• Antibodies, identified by ELISA testing, rose in serum from 6 dpi and continued rising throughout the observation period. They were stimulated more by re-inoculation, suggesting that the immune system adjusts its response based on the severity of the viral attack.
• The study also noted a rise in virus neutralizing antibodies from day 14, which increased parallelly to the total ELISA antibody, implying simultaneous development of specific and broad-spectrum immune responses against the virus.

Analysis of Cellular Immunity

• Cellular immunity was analyzed using the Antibody Dependent Cytotoxicity (ADCC) test and a specific lymphocyte transformation test. These tests revealed that the ability of foal neutrophils to effect ADCC decreased significantly between 3 to 10 days after inoculation. This indicates that the initial robust immune response could be reducing with time or as the body “learns” to manage the infection.
• Peripheral blood mononuclear cells (PBMC), a type of immune cell, showed reactivity to EHV-1 antigens from day 14, peaking between 28 and 42 dpi. This suggests that the body’s cellular immunity takes some time to mount a full response, but when it does, it can effectively fight the virus.