Kaposiís Sarcoma-associated Herpesvirus Targets Subepithelial B Cells
Lynn Hassman* and D Kedes
Univ of Virginia, Charlottesville, US
Background: †Kaposiís sarcoma-associated herpesvirus
(KSHV) is a tumorigenic virus that establishes lifelong infection in the human
host by infecting B cells and expresses viral proteins capable of modulating B
cell signaling and survival. KSHV infection in an immunocompromised host
results in several tumors, including 2 B cell dyscrasias (multicentric
Castlemanís disease, and primary effusion lymphoma). To date, the only clues to
the identity of the human B cell subsets that may represent the earliest targets
during KSHV transmission are inferences based on the phenotypic
characterization of KSHV+ lymphomas. Another hint, however, may come
from Chagasí et al. (2006) histological study of human tonsils, which found
KSHV+ cells localized to the region beneath the tonsillar crypts.
Since this area is populated by a unique subset of B cells (subepithelial B
cells) and epidemiologic data support salivary transmission of KSHV, we
hypothesized that subepithelial B cells may represent an initial entry point,
as well as a long-term reservoir for the virus. The surface marker phenotype of
multicentric Castlemanís disease is consistent with this hypothesis.
Identification and characterization of B cell subsets infected by KSHV may shed
light into the mechanisms of KSHV transmission as well as the genesis of
KSHV-induced tumors in patients with AIDS or other immune deficiencies.
Methods: †We exposed cultures of purified tonsillar B
cells to KSHV and then used multispectral imaging fluorescence cytometry
(Imagestream, Amnis), a high through-put method for analyzing both immunofluorescence
and morphological parameters to analyzed the surface marker phenotype of cells
expressing the major latent viral protein.
Results: †We found that between 1% and 16% of human
tonsillar B cells became infected upon exposure to KSHV, that these infected B
cells were immunoglobulin (Ig) Mhi, IgDlo, and CD5+
and that CD5 expression increased between 48 and 72 hours post inoculation.
Furthermore, KSHV-infected cells were restricted to those expressing the lambda
immunoglobulin light chain.
Conclusions: †The phenotype of B cells infected with
KSHV in vitro corresponds to activated (CD5+) subepithelial
(IgMhi, IgDlo) B cells. Additionally, the
lambda-restriction of KSHV-infected subepithelial B cells mirrors this
phenotype in multicentric Castlemanís disease. These data suggest that KSHV
preferentially infects subepithelial B cells ex vivo, implying that
there may be both functional as well as anatomic aspects of this population
that favor infection.