Mycoplasma bovis-Induced Inhibition of Bovine Peripheral Blood Mononuclear Cell Proliferation Is Ameliorated after Blocking the Immune-Inhibitory Programmed Death 1 Receptor

Abstract

-induced immune suppression is a major obstacle faced by the host for controlling infections. impairment of antigen-specific T-cell responses is achieved through inhibiting the proliferation of peripheral blood mononuclear cells (PBMCs). This impairment may contribute to the persistence of infection in various sites, including lungs, and its systemic spread to various organs such as joints, with the underlying mechanisms remaining elusive. Here, we elucidated the role of the immune-inhibitory receptor programmed death 1 (PD-1) and its ligand (PD-L1) in infection. Flow cytometry (FCM) analyses revealed an upregulation of PD-L1 expression on tracheal and lung epithelial cell lines after infection. In addition, we found increased PD-L1 expression on purified lung lavage macrophages following infection by FCM and determined its localization by immunofluorescence analysis comparing infected and control lung tissue sections. Moreover, infection increased the expression of the PD-1 receptor on total PBMCs and in gated CD4 and CD8 T-cell subpopulations. We demonstrated that infection induced a significant decrease in CD4 PD-1 and CD8 PD-1 subsets with intermediate PD-1 expression, which functioned as progenitor pools giving rise to CD4 PD-1 and CD8 PD-1 subsets with high PD-1 expression levels. We blocked PD-1 receptors on PBMCs using anti-PD-1 antibody at the beginning of infection, leading to a significant restoration of the proliferation of PBMCs. Taken together, our data indicate a significant involvement of the PD-1/PD-L1 inhibitory pathway during infection and its associated immune exhaustion, culminating in impaired host immune responses.

Bovine Epithelial in vitro Infection Models for Mycoplasma bovis

“…High amounts of strain L22/93 associated with cells even led to an anti-proliferative response of primary epithelial cells. The same observation was also previously made with PBMCs (Suleman et al, 2018 ). However, the in vivo relevance of this finding is not clear.…”

“…Infected PBMCs were studied, considering cytotoxic effects, induction of apoptosis and viability of host cells, but results were inconsistent (Vanden Bush and Rosenbusch, 2002 ; van der Merwe et al, 2010 ; Gondaira et al, 2015 ). However, M. bovis was shown to inhibit proliferation of PBMCs (Vanden Bush and Rosenbusch, 2002 ; van der Merwe et al, 2010 ; Suleman et al, 2016 , 2018 ). Studies analyzing distinct blood cell types gave clearer results.…”

Humoral and Cell-Mediated Immune Response Validation in Calves after a Live Attenuated Vaccine of Babesia bigemina

“…Bovine leukemia virus causes progressive exhaustion of T cell functions by up-regulation of programmed death-1 (PD-1) and lymphocyte activation gene-3 [ 42 ], and blockage of its receptor PD-L1 leads to enhancement of antiviral responses [ 43 ]. Certain bovine respiratory complex pathogens like Mycoplasma bovis strongly inhibit lymphoproliferation of CD4+ and CD8+ T cells during infection [ 44 ]. Anaplasma marginale is also known to downregulate antigen-specific T and B cells leading to a failure to establish effective memory T cell responses and persistent infection [ 45 ].…”

Immune Evasion of Mycoplasma bovis

“…T-cells showed a substantial decrease in CD4 PD1 and CD8 PD1 subsets and a significant increase in CD4 PD1 and CD8 PD1 subsets. Furthermore, the use of blocking PD-1 antibodies results in the restoration of M. bovis strain Mb1 after PD-1/PD-L1 destruction as well as the proliferation of M. bovis strain Mb1 in contaminated PBMCs [ 31 ]. A recent study showed that PD-1/PD-L1 ( Figure 3 ) is important for Mycoplasma bovis pathogenesis and related immune exhaustion in inhibitory pathways, resulting in compromised host immune responses [ 31 ].…”

“…Inconsistent findings on PBMC contamination by M. bovis have been obtained regarding apoptosis induction, cytotoxic effects, and the host cells’ viability [ 8 , 28 , 29 , 30 ]. Similarly, Mycoplasma bovis has been found to inhibit the development of PBMCs [ 8 , 29 , 31 , 32 ].…”