B Cells in Early Rheumatoid Arthritis: ZAP-70 More Than SYK Characterize Seropositive Disease

Background/Purpose: B cells are involved as central players in the
pathogenesis of rheumatoid arthritis (RA). Our aim was to define whether a
specific B cell subset characterizes the early phases of the disease and is
associated with a peculiar RA phenotype.
Methods: 105 ERA patients (81.0% females; mean age 54.7 15.2
years; 73.3% autoantibodies-AAB positive) and 30 healthy controls (HC)
were studied. Baseline clinical and immunological characteristics and inflammatory
status were assessed. Peripheral blood samples were analyzed by flow
cytometry for the distribution of circulating B cell subsets by staining with
surface markers CD19, CD45, CD38, CD27 and IgD and intracellular marker
ZAP70. Plasma levels of IL-6 and BAFF were also determined with ELISAs.
The expression of ZAP-70 and SYK was analized in B cells of 22 ERA
patients, using the RealTime ready Assay method.
Results: ERA patients showed a higher percentage of naı¨ve-activate B
cells and a lower percentage of memory B cells compared to HC, as
confirmed by a higher ratio between Bm2 Bm2’/eBm5 Bm5 (3.4 3.5 in
ERA and 1.7 0.9 in controls, p 0.003). AAB positive patients showed a
higher percentage of CD19 /CD38 CD27 (4.0 5.0%) compared to
AAB negative ones (2.2 2.8%, p 0.05). The expression of ZAP-70 in B
cells was similar in ERA patients and controls. Dividing patients for the AAB
seropositivity, AAB ERA patients showed higher percentage of CD19 /
ZAP70 cells compared to AAB- (5.1 6.3 vs 2.5 2.4, p 0.01) and also to
HC (2.2 1.4, p 0.05). In ERA patients, the percentage of ZAP70 B cells
correlated directly with the percentage of CD19 /IgD-CD27- cells (r 0.338,
p 0.001), plasma BAFF levels (r 0.26, p 0.01) and with Anti-MCV
(r 0.27, p 0.01), ACPA (r 0.23, p 0.02) and RF-IgA (r 0.28, p 0.01)
AAB titers. ZAP-70 transcription in B cells of subjects seropositive for
autoantibodies was significantly higher than in seronegative ones (3.4 2.8
vs 1.2 1.0 respectively; p 0.04), data confirmed by an higher ratio
ZAP70/SYK in AB compared to AB- (2.9 1.6 vs 1.2 1.0 respectively;
p 0.01). Moreover, the expression of ZAP-70 correlated positively with the
expression of SYK (r 0.66, p 0.003) and showed a trend for an association
with the espression of ZAP70 protein, evaluated by flow-cytometry (r 0.41,
p 0.09).
Conclusion: ZAP-70 positive B cells characterize AAB positive RA and
the expression of ZAP-70 might be a possible complementary biomarker of
seropositive disease.