Transfusion of hyperimmune plasma for protecting foals againstRhodococcus equipneumonia

Abstract

The bacterium Rhodococcus equi causes pneumonia in foals that is prevalent at breeding farms worldwide. In the absence of an effective vaccine, transfusion of commercial plasma from donor horses hyperimmunised against R. equi is used by many farms to reduce the incidence of pneumonia among foals at farms where the disease is endemic. The effectiveness of hyperimmune plasma for controlling R. equi pneumonia in foals has varied considerably among reports. The purposes of this narrative review are: (1) to review early studies that provided a foundational basis for the practice of transfusion of hyperimmune plasma that is widespread in the United States and in many other countries; (2) to summarise current knowledge of hyperimmune plasma for preventing R. equi pneumonia; (3) to provide an interpretive summary of probable explanations for the variable results among studies evaluating the effectiveness of transfusion of hyperimmune plasma for reducing the incidence of R. equi pneumonia; (4) to review mechanisms by which hyperimmune plasma might mediate protection; and (5) to consider risks of transfusing foals with hyperimmune plasma. Although the weight of evidence supports the practice of transfusing foals with hyperimmune plasma to prevent R. equi pneumonia, many important gaps in our knowledge of this topic remain including the volume/dose of hyperimmune plasma to be transfused, the timing(s) of transfusion, and the mechanism(s) by which hyperimmune plasma mediates protection. Transfusing foals with hyperimmune plasma is expensive, labourintensive, and carries risks for foals; therefore, alternative approaches for passive and active immunisation to prevent R. equi pneumonia are greatly needed.

Protective immune responses against Rhodococcus equi : an innate immunity-focused review

“…Furthermore, the adaptive response also enhances bacterial killing by innate cells. 19,118,[196][197][198][199] Cell-mediated immunity Professional phagocytic cells such as macrophages, dendritic cells, and neutrophils recognize microorganisms through PRRs and ingest them into phagosomes, which acidify and eventually fuse with lysosomes, exposing the microorganisms to a microbicidal environment. 200,201 Next, digested microbial antigens are presented through MHC class II and concomitant expression of co-stimulatory molecules to stimulate adaptive cellular immunity.…”

“…Humoral immunity appears to play a role in protecting against R. equi pneumonia and increasing the effectiveness of innate immune cells for killing R. equi . [196][197][198][199] Opsonization ofR. equi with serum containing high R. equi -specific antibody activity increases bacterial killing by equine neutrophils more than serum with low R. equi -specific antibody activity.…”

Impact of surface receptors TLR2, CR3, and FcγRIII on Rhodococcus equi phagocytosis and intracellular survival in macrophages

“…R. equi opsonization with serum or plasma increases phagocytosis and bacterial killing by phagocytes, but these effects might be attributable to complement, antibodies, or other serum components ( 14 , 37 – 40 ). Protection against R. equi pneumonia induced by specific hyperimmune plasma (HIP) transfusion in newborns has been attributed primarily to the presence of R. equi -specific antibodies, in particular IgG ( 41 – 46 ). In vitro opsonization with either HIP or standard plasma (from donors not hyperimmunized against R. equi ) decreased intracellular survival of R. equi , but the mechanisms by which standard plasma or HIP protect against in vitro infection are poorly understood ( 39 , 41 ).…”

Evaluation of vaccine candidates against Rhodococcus equi in BALB/c mice infection model: cellular and humoral immune responses

“…The inactivated vaccine ensures the structural integrity of R. equi and can induce humoral and cellular immune responses in foals, but it is not effective in protecting foals from the challenge of virulent R. equi [ 15 , 16 ]. To date, the only licenced approach to reduce the incidence and severity of R. equi pneumonia is prophylactic transfusion of R. equi -specific hyperimmune plasma, but the results of this approach in experimental and field studies are conflicting [ 17 , 18 ]. Indeed, similar to Mycobacterium tuberculosis ( M. tb ), the cellular immune response against this intracellular bacterium pathogen is largely thought to exert major immune protection, although the antibody response also mediates immune protection [ 19 , 20 ].…”