Despite 25 years of research, the basic virology of Kaposi Sarcoma Herpesviruses (KSHV) in B lymphocytes remains poorly understood. This study seeks to fill critical gaps in our understanding by characterizing the B lymphocyte lineage-specific tropism of KSHV. Here, we use lymphocytes derived from 40 human tonsil specimens to determine the B lymphocyte lineages targeted by KSHV early during de novo infection in our ex vivo model system. We characterize the immunological diversity of our tonsil specimens and determine that overall susceptibility of tonsil lymphocytes to KSHV infection varies substantially between donors. We demonstrate that a variety of B lymphocyte subtypes are susceptible to KSHV infection and identify CD138+ plasma cells as a highly targeted cell type for de novo KSHV infection. We determine that infection of tonsil B cell lineages is primarily latent with few lineages contributing to lytic replication. We explore the use of CD138 and heparin sulfate proteoglycans as attachment factors for the infection of B lymphocytes and conclude that they do not play a substantial role. Finally, we determine that the host T cell microenvironment influences the course of de novo infection in B lymphocytes. These results improve our understanding of KSHV transmission and the biology of early KSHV infection in a naïve human host, and lay a foundation for further characterization of KSHV molecular virology in B lymphocyte lineages.

1Despite 25 years of research, the basic virology of Kaposi Sarcoma Herpesviruses 2 (KSHV) in B lymphocytes remains poorly understood. This study seeks to fill critical 3 gaps in our understanding by characterizing the B lymphocyte lineage-specific tropism 4 of KSHV. Here, we use lymphocytes derived from 40 human tonsil specimens to 5

The virion proteins of Kaposi sarcoma-associated herpesvirus (KSHV) were initially characterized in 2005 in two separate studies that combined the detection of 24 viral proteins and a few cellular components via LC-MS/MS or MALDI-TOF. Despite considerable advances in the sensitivity and specificity of mass spectrometry instrumentation in recent years, leading to significantly higher yields in detections, the KSHV virion proteome has not been revisited. In this study, we have re-examined the protein composition of purified KSHV virions via ultra-high resolution Qq time-of-flight mass spectrometry (UHR-QqTOF). Our results confirm the detection of all previously reported virion proteins, in addition to 17 other viral proteins, some of which have been characterized as virion-associated using other methods, and 10 novel proteins identified as virion-associated for the first time in this study. These results add KSHV ORF9, ORF23, ORF35, ORF48, ORF58, ORF72/vCyclin, K3, K9/vIRF1, K10/vIRF4, and K10.5/vIRF3 to the list of KSHV proteins that can be incorporated into virions. The addition of these proteins to the KSHV virion proteome provides novel and important insight into early events in KSHV infection mediated by virion-associated proteins. Data are available via ProteomeXchange with identifier PXD022626.

Kaposi’s sarcoma-associated herpesvirus (KSHV) extensively manipulates the host immune system and the cytokine milieu, and cytokines are known to influence the progression of KSHVassociated diseases. However, the precise role of cytokines in the early stages of KSHV infection remains undefined. Here, using our unique model of KSHV infection in tonsil lymphocytes, we investigate the influence of host cytokines on the establishment of KSHV infection in B cells. Our data demonstrate that KSHV manipulates the host cytokine microenvironment during early infection and susceptibility generally associated with downregulation of multiple cytokines. However, we show that IL-21 signaling promotes KSHV infection by promoting both plasma cell numbers and increasing KSHV infection in plasma cells. Our data reveal that IL-21 producing T cells, particularly Th17/Tc17 and central memory CD8+ T cells may represent immunological factors that modulate host-level susceptibility to KSHV infection. These results suggest that IL-21 plays a significant role in the early stages of KSHV infection in the human immune system and may represent a novel mechanism to be further explored in the context of preventing KSHV transmission.

No abstract