associated myelopathy (HAM). The pathogenesis of HAM is not fully understood.
However, considerable evidence points to the importance of the regulatory protein
Tax. Tax promotes the proliferation of HTLV-1 infected cells but also induces a
strong cytotoxic-T-lymphocyte response. The contribution of the HTLV-1 basic
leucine zipper protein (HBZ), which promotes T cell proliferation but suppresses
Tax mediated transactivation, remains to be elucidated.
This thesis explores the following hypotheses:-
1. HBZ is expressed in vivo and will elicit an immune response in HTLV-1
infected subjects.
2. HBZ mRNA will be detected in peripheral blood mononuclear cells
(PBMCs) from HTLV-1 infected subjects.
To test these hypotheses 48 subjects: 14 patients with HAM, 28 asymptomatic
carriers (ACs) (14 with high viral load >1% and 14 with low viral load <1%), and six
HTLV-1 negative individuals were studied. PBMCs and plasma were isolated from
whole blood and preserved for future use.
The first hypothesis was addressed by developing HBZ and Tax enzyme linked
immuno spot assays (ELIspot) with overlapping peptides that span the entire
proteins. The frequency of Tax-specific and HBZ-specific CD4+ and CD8+ T cells
secreting IFN- or IL-2 were compared. The presence of any HBZ-specific CD8+
IL-2 secreting T cell response was most commonly detected in ACs with low viral
load. Tax-specific CD8+ IL-2 secreting T cell responses were most commonly
detected in patients with HAM but where detected the number of IFN- secreting
Tax-specific CD8 cells was highest in patients with HAM. No significant difference
in CD4+ T cell responses was observed.
The second hypothesis was tested by developing real-time PCR to detect and
quantify HBZ and Tax mRNA. HBZ mRNA was detected in PBMCs from patients
with high viral load regardless of disease whilst Tax mRNA was only detected in
three patients, all with HAM. HTLV-1 viral load correlated positively with HBZ
mRNA, but not Tax.
At this point, two new hypotheses were considered: -
3. The cytokine profile differs between patients with HAM and ACs.
4. Cytokine profile and ELIspot frequency will be altered during in vivo
treatment with immunomodulators.The cytokine profile was examined in a subset of 12 patients using a commercial
electrochemiluminescence assay that simultaneously quantifies nine
proinflammatory cytokines. GM-CSF, IL-12-p70 and IL-8 were disease associated.
IFN-, IL10, IL-6 and TNF- were viral load dependent. IL-1and IL-2 did not
discriminate. In vivo treatment with Infliximab and Ciclosporin A did not
significantly alter the cytokine profiles.
In conclusion, a detectable HBZ response is associated with an absence of HBZ
mRNA and is most common in AC with low viral load. The absence of HBZ
responses is associated with detectable HBZ mRNA and the presence of Tax
responses and is associated with high viral load and the presence of HAM.