Identification of immunologically relevant genes in mare and foal dendritic cells responding to infection by Rhodococcus equi.

This study focused on identifying key genes in horse and foal dendritic cells that respond to infections from the bacteria Rhodococcus equi. The identified genes could potentially explain the varying susceptibility to the disease in foals versus adult horses.

Background

• Rhodococcus equi is a bacteria that lives inside cells of a host organism and has significant impact on horses. While adult horses mostly remain unaffected, infected foals often suffer from pyogranulomatous pneumonia — a severe lung infection that’s characterized by inflammation and the formation of granulomas (clusters of immune cells).
• The bacteria infect and multiply within the macrophages and dendritic cells (DCs) of the host. DCs are immune cells that trigger an adaptive immune response, thus playing a vital role in determining whether an infection is successfully managed by the body or not.

Research Aim

• The goal of this research was to identify any genes in monocyte-derived dendritic cells (mdDCs) that display different behavior or expression when infected with R. equi.
• Monocytes are a type of immune cell that can differentiate into other types of cells such as mdDCs. The researchers cultured mdDCs from blood samples from mares and foals in an environment supplemented with recombinant equine IL-4 and recombinant human GM-CSF. These are growth factors that encourage the differentiation and growth of monocytes into mdDCs.

Methodology and Results

• The researchers infected the cultivated mdDCs with R. equi and isolated the RNA from these cells 24 hours later. Using a technique known as suppression subtractive hybridization (SSH), they were able to identify different sequences of genes between the infected and non-infected mdDCs.
• From their experiment, the team identified around 38 unique gene sequences. They further validated the differential expression of 19 relevant genes using a method known as PCR (polymerase chain reaction), which can amplify specific DNA or RNA sequences and thus confirm their presence.
• The identified genes were associated with various functions including cell adhesion, migration, immune response, ion transport, signal transduction, T-cell regulation, and vesicular transport.

Conclusion

• This research has brought the identification of several new genes that behave differently in the dendritic cells of foals and adult horses when infected with R. equi.
• This information opens up a new avenue of research to understand the body’s response to R. equi and why foals are especially susceptible to the disease.