Adiba Isa

Slow Clearance of Human Parvovirus B19 Viremia following Acute Infection

Parvovirus B19 is a common, clinically significant pathogen. Reassessment of the viral kinetics after acute infection showed that the virus is not rapidly cleared from healthy hosts, despite early resolution of symptoms. These findings challenge our current conception of the virus pathogenesis and have implications for the management of the infection.

Prolonged activation of virus-specific CD8+T cells after acute B19 infection.

Background Human parvovirus B19 (B19) is a ubiquitous and clinically significant pathogen, causing erythema infectiosum, arthropathy, transient aplastic crisis, and intrauterine fetal death. The phenotype of CD8+ T cells in acute B19 infection has not been studied previously. Methods and Findings The number and phenotype of B19-specific CD8+ T cell responses during and after acute adult infection was studied using HLA–peptide multimeric complexes. Surprisingly, these responses increased in magnitude over the first year post-infection despite resolution of clinical symptoms and control of viraemia, with T cell populations specific for individual epitopes comprising up to 4% of CD8+ T cells. B19-specific T cells developed and maintained an activated CD38+ phenotype, with strong expression of perforin and CD57 and downregulation of CD28 and CD27. These cells possessed strong effector function and intact proliferative capacity. Individuals tested many years after infection exhibited lower frequencies of B19-specific cytotoxic T lymphocytes, typically 0.05%–0.5% of CD8+ T cells, which were perforin, CD38, and CCR7 low. Conclusion This is the first example to our knowledge of an “acute” human viral infection inducing a persistent activated CD8+ T cell response. The likely explanation—analogous to that for cytomegalovirus infection—is that this persistent response is due to low-level antigen exposure. CD8+ T cells may contribute to the long-term control of this significant pathogen and should be considered during vaccine development.

Sustained CD8+ T-Cell Responses Induced after Acute Parvovirus B19 Infection in Humans

ABSTRACT Murine models have suggested that CD8+ T-cell responses peak early in acute viral infections and are not sustained, but no evidence for humans has been available. To address this, we longitudinally analyzed the CD8+ T-cell response to human parvovirus B19 in acutely infected individuals. We observed striking CD8+ T-cell responses, which were sustained or even increased over many months after the resolution of acute disease, indicating that CD8+ T cells may play a prominent role in the control of parvovirus B19 and other acute viral infections of humans, including potentially those generated by live vaccines.

Tracking of Peptide-Specific CD4+ T-Cell Responses after an Acute Resolving Viral Infection: a Study of Parvovirus B19

ABSTRACT The evolution of peptide-specific CD4+ T-cell responses to acute viral infections of humans is poorly understood. We analyzed the response to parvovirus B19 (B19), a ubiquitous and clinically significant pathogen with a compact and conserved genome. The magnitude and breadth of the CD4+ T-cell response to the two B19 capsid proteins were investigated using a set of overlapping peptides and gamma interferon-specific enzyme-linked immunospot assays of peripheral blood mononuclear cells (PBMCs) from a cohort of acutely infected individuals who presented with acute arthropathy. These were compared to those for a cohort of B19-specific immunoglobulin M-negative (IgM−), IgG+ remotely infected individuals. Both cohorts of individuals were found to make broad CD4+ responses. However, while the responses following acute infection were detectable ex vivo, responses in remotely infected individuals were only detected after culture. One epitope (LASEESAFYVLEHSSFQLLG) was consistently targeted by both acutely (10/12) and remotely (6/7) infected individuals. This epitope was DRB1*1501 restricted, and a major histocompatibility complex peptide tetramer stained PBMCs from acutely infected individuals in the range of 0.003 to 0.042% of CD4+ T cells. Tetramer-positive populations were initially CD62Llo; unlike the case for B19-specific CD8+ T-cell responses, however, CD62L was reexpressed at later times, as responses remained stable or declined slowly. This first identification of B19 CD4+ T-cell epitopes, including a key immunodominant peptide, provides the tools to investigate the breadth, frequency, and functions of cellular responses to this virus in a range of specific clinical settings and gives an important reference point for analysis of peptide-specific CD4+ T cells during acute and persistent virus infections of humans.

A Highly Restricted T-Cell Receptor Dominates the CD8+ T-Cell Response to Parvovirus B19 Infection in HLA-A*2402-Positive Individuals

ABSTRACT Six of seven HLA-A*2402-positive individuals with acute parvovirus B19 infections made vigorous CD8-positive cytotoxic T-cell (CTL) responses to the viral epitope FYTPLADQF. All responders showed highly focused T-cell receptor (TCR) usage, using almost exclusively BV5.1. The BV5.1 TCR dominated the acute response, was maintained over time, and was also used by a remotely infected individual. Nine CTL clones and two oligoclonal lines obtained from three unrelated individuals used BV5.1, BJ2.1, and a conserved TCR CDR3 of nine amino acids. This commonly recognized epitope is likely important in long-term protective immunity and should be included in vaccine design.

Cytokine responses in acute and persistent human parvovirus B19 infection

The aim of this study was to characterize the proinflammatory and T helper (Th)1/Th2 cytokine responses during acute parvovirus B19 (B19) infection and determine whether an imbalance of the Th1/Th2 cytokine pattern is related to persistent B19 infection. Cytokines were quantified by multiplex beads immunoassay in serum from B19‐infected patients and controls. The cytokine responses were correlated with B19 serology, quantitative B19 DNA levels and clinical symptoms. In addition to a proinflammatory response, elevated levels of the Th1 type of cytokines interleukin (IL)‐2, IL‐12 and IL‐15 were evident at time of the initial peak of B19 viral load in a few patients during acute infection. This pattern was seen in the absence of an interferon (IFN)‐γ response. During follow‐up (20–130u2003weeks post‐acute infection) some of these patients had a sustained Th1 cytokine response. The Th1 cytokine response correlated with the previously identified sustained CD8+ T cell response and viraemia. A cross‐sectional study on patients with persistent B19 infection showed no apparent imbalance of their cytokine pattern, except for an elevated level of IFN‐γ response. No general immunodeficiency was diagnosed as an explanation for the viral persistence in this later group. Neither the acutely infected nor the persistently infected patients demonstrated a Th2 cytokine response. In conclusion, the acutely infected patients demonstrated a sustained Th1 cytokine response whereas the persistently infected patients did not exhibit an apparent imbalance of their cytokine pattern except for an elevated IFN‐γ response.

Mapping of the Ex Vivo Cellular Immune Response Against the Complete Human Parvovirus B19 Genome During Acute Infection

Background:u2002 Human parvovirus B19 (B19) is a ubiquitous pathogen, normally causing a mild self‐limiting disease, but also capable of causing both significant pathology and long‐term persistence. The small size and stability of the virus makes it suitable for mapping of the full breath and the kinetics of the cellular immune responses following acute viral infection. Methods:u2002 Five patients with acute primary B19 infection were included in the study and followed consecutively for up to 200 weeks. Cellular immune responses were mapped by IFNγ enzyme‐linked immunospot to overlapping peptides spanning the whole B19 genome. Results:u2002 In all five acutely infected patients, we were able to monitor the kinetics of a strong specific cellular immune reaction. Responses peaked at levels of 850–1850 SFC/million PBMCs, roughly corresponding to 0.3–0.6% B19‐specific CD8+ cells circulating in peripheral blood at 10–80 weeks post‐infection. The responses in individual patients were directed to three or four different peptide pools, and the specificity was confined to the same CD8 epitopes present in the pools throughout the follow‐up period. The majority of responses were directed to the virus nonstructural protein, only two patients showed any response to the capsid proteins, elicited by the same epitope in both cases. Conclusion:u2002 The cellular immune responses to acute B19 infection are surprisingly narrow in distribution and remain at high levels for up to 80 weeks post‐infection. The initial epitope specificity is maintained, and the majority of responses target the virus nonstructural protein, which is not included in vaccine preparations, evaluated against the infection.