Rhodococcus equi-Specific Cytotoxic T Lymphocytes in Immune Horses and Development in Asymptomatic Foals

Abstract

Rhodococcus equi is an important cause of pneumonia in young horses; however, adult horses are immune due to their ability to mount protective recall responses. In this study, the hypothesis that R. equi-specific cytotoxic T lymphocytes (CTL) are present in the lung of immune horses was tested. Bronchoalveolar lavage (BAL)-derived pulmonary T lymphocytes stimulated with R. equi lysed infected alveolar macrophages and peripheral blood adherent cells (PBAC). As with CTL obtained from the blood, killing of R. equi-infected targets by pulmonary effectors was not restricted by equine lymphocyte alloantigen-A (ELA-A; classical major histocompatibility complex class I), suggesting a novel or nonclassical method of antigen presentation. To determine whether or not CTL activity coincided with the age-associated susceptibility to rhodococcal pneumonia, CTL were evaluated in foals. R. equi-stimulated peripheral blood mononuclear cells (PBMC) from 3-week-old foals were unable to lyse either autologous perinatal or mismatched adult PBAC targets. The defect was not with the perinatal targets, as adult CTL effectors efficiently killed infected targets from 3-week-old foals. In contrast, significant CTL activity was present in three of five foals at 6 weeks of age, and significant specific lysis was induced by PBMC from all foals at 8 weeks of age. As with adults, lysis was ELA-A unrestricted. Two previously described monoclonal antibodies, BCD1b3 and CD1F2/1B12.1, were used to examine the expression of CD1, a nonclassical antigen-presenting molecule, on CTL targets. These antibodies cross-reacted with both foal and adult PBAC. However, neither antibody bound alveolar macrophages, suggesting that the R. equi-specific, major histocompatibility complex-unrestricted lysis is not restricted by a surface molecule identified by these antibodies.

Foal Monocyte-Derived Dendritic Cells Become Activated uponRhodococcus equiInfection

“…It is important to consider that a protective immune response is the result of combination and interaction among the many arms of the immune system (innate and acquired mechanisms). Indeed, foal mMOs revealed a measurable response to R. equi infection and other studies have shown their competence at interacting with cytotoxic lymphocytes (44,64).…”

Identification of Rhodococcus equi lipids recognized by host cytotoxic T lymphocytes

“…A subsequent study confirmed the presence of R. equispecific, MHC class I-unrestricted CTLs in foals (Patton et al, 2005). However, CTLs were not present during the first few weeks of life -the period at which foals are considered most susceptible and probably first infected.…”

“…The following formula for percentage specific lysis was used: [(E2S)/(T2S)]6100, where E is the mean of three test wells, S is the mean spontaneous release from three target cell wells without effector cells, and T is the mean total release from three target cell wells with 2 % Triton X-100 (Sigma-Aldrich). As reported previously, significant lysis was defined as 3 SEM above the negative-control value (McGuire et al, 1994;Patton et al, 2004Patton et al, , 2005Siliciano et al, 1985).…”

“…Importantly, the R. equi-specific, ELA-A-unrestricted CTLs were shown not to be present when foals are most susceptible to rhodococcal pneumonia (i.e. the first few weeks of life) and then appeared as foals matured -presumably reflecting a developing adaptive immune response (Patton et al, 2005). Whilst this work defined the lymphocyte population involved in a potentially protective immune response in horses and showed a correlation between the presence of CTLs and age-associated susceptibility, it did not define the bacterial antigen(s) involved.…”

Cloning and large-scale expansion of epitope-specific equine cytotoxic T lymphocytes using an anti-equine CD3 monoclonal antibody and human recombinant IL-2

“…Cytotoxic T lymphocytes are involved in the control of several important intracellular pathogens of horses, including equine herpes virus-1 (1-7), equine arteritis virus (8), and Rhodococcus equi (9,10). In horses infected with equine infectious anemia virus (EIAV), a lentivirus with a world-wide distribution, CTL are critical in the control of viral replication and clinical disease (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22).…”