B cells and platelets harbor prion infectivity in the blood of deer infected with chronic wasting disease

Abstract

Substantial evidence for prion transmission via blood transfusion exists for many transmissible spongiform encephalopathy (TSE) diseases. Determining which cell phenotype(s) is responsible for trafficking infectivity has important implications for our understanding of the dissemination of prions, as well as their detection and elimination from blood products. We used bioassay studies of native white-tailed deer and transgenic cervidized mice to determine (i) if chronic wasting disease (CWD) blood infectivity is associated with the cellular versus the cell-free/plasma fraction of blood and (ii) in particular if B-cell (MAb 2-104(+)), platelet (CD41/61(+)), or CD14(+) monocyte blood cell phenotypes harbor infectious prions. All four deer transfused with the blood mononuclear cell fraction from CWD(+) donor deer became PrP(CWD) positive by 19 months postinoculation, whereas none of the four deer inoculated with cell-free plasma from the same source developed prion infection. All four of the deer injected with B cells and three of four deer receiving platelets from CWD(+) donor deer became PrP(CWD) positive in as little as 6 months postinoculation, whereas none of the four deer receiving blood CD14(+) monocytes developed evidence of CWD infection (immunohistochemistry and Western blot analysis) after 19 months of observation. Results of the Tg(CerPrP) mouse bioassays mirrored those of the native cervid host. These results indicate that CWD blood infectivity is cell associated and suggest a significant role for B cells and platelets in trafficking CWD infectivity in vivo and support earlier tissue-based studies associating putative follicular B cells with PrP(CWD). Localization of CWD infectivity with leukocyte subpopulations may aid in enhancing the sensitivity of blood-based diagnostic assays for CWD and other TSEs.

FIG. 1.

Terminal lymphoid and brain (medulla at obex) IHC analysis results of naïve deer cohorts inoculated with CWD⁺ blood components. PrP^CWD demonstrated by IHC analysis in tonsil, brain (medulla oblongata at obex), and retropharyngeal lymph node tissues of deer receiving whole blood, cell fraction, B cells, or CD41/61⁺ cells from CWD-infected donors. Arrows indicate PrP^CWD staining (red) within the brain and lymphoid follicles. The arrow with the asterisk indicates a lymphoid follicle negative for PrP^CWD.

FIG. 2.

WB analysis of cohorts of naïve deer inoculated with CWD⁺ blood components. WB demonstration of the typical PK digestion band shift (28 to 35 kDa) associated with prion infection (medulla at obex) of deer receiving whole blood, mononuclear cell fraction, B cells, or CD41/61⁺ cells. Deer receiving cell-free plasma or CD14⁺ cells from CWD-infected donors remained PrP^CWD negative. Lanes 1 to 4 represent CWD⁺/CWD⁻ deer controls (10% brain homogenate) without and with PK digestion at 25 μg/ml. Lanes 5 to 16, 10% brain homogenate of whole-blood-, mononuclear-cell-, plasma-, B-cell-, CD41/61⁺-, or CD14⁺-inoculated deer without and with PK digestion at 25 μg/ml.

FIG. 3.

Brain IHC analysis results for Tg(CerPrP-E226)5037^+/− mice inoculated with CWD⁺ blood components. PrP^CWD demonstrated by IHC analysis in sagittal brain sections of Tg(CerPrP-E226)5037^+/− mice receiving whole blood, cell fraction, CD41/61⁺, or B cells from CWD-infected donors. PrP^CWD plaque deposits are typical of those previously described in CWD infection in white-tailed deer (69) and Tg(CerPrP-E226)5037^+/− mice (28).

FIG. 4.

Attack rates in Tg(CerPrP-E226)5037^+/− mice intracranially inoculated with CWD⁺ blood components. Shown are the percentages of Tg(CerPrP-E226)5037^+/− mice that developed prion disease after i.c. inoculation with brain tissue (⧫), B cells (-), whole blood (▴), cell fraction (▪), platelets (•), cell-free plasma (□), or monocytes (○) from CWD-infected donor deer or brain tissue from a CWD⁻ donor deer (⋄).