3%HEALTHY CONTROL PSS PATIENT WITH NHLPSS PATIENT #13 PSS PATIENT #...

94.3%Healthy Control pSS patient with NHLpSS patient #13 pSS patient #5

CD19

Analysis of the distribution of peripheral CD19

⁺

B cell subsets demonstrates that patients with primary Sjưgren’s syndrome (pSS) have reduced

frequencies of CD27

⁺

memory B cells in the peripheral blood compared with normal donors. In addition, patients with pSS with secondary non-

Hodgkin lymphoma exhibited an increase in CD27

⁺

B cells in the blood.

Figure 2

Normals

Systemic Lupus Lupus

Sjưgren‘s ’s

Systemic

Sjưgren

syndrome

Plasmablasts

Plasmablasts

Nạve

Nạve

Memory

B cells

Memory

B cells 60%

^Memory

B cells 60%

B cells ≥ 80%

Memory B cells

B cells 80%

B cells

CD27 Expression

Schematic distribution of B cell subsets in peripheral blood of normals compared with patients with systemic lupus erythematosus and Sjưgren’s

syndrome.

(P < 0.05) or patients with SLE (P < 0.0002). Another

ited significant decreases in peripheral B cell frequencies

recent study [57] characterized peripheral B cells in 11

[33,40]. In one study [57], patients with RA also manifested

patients with pSS as well as patients with RA and normal

an increased frequency of CD27

⁺

memory B cells and a

normal frequency of CD27

^–

naive B cells. The pattern of B

controls. These investigators also found a predominance

of naive B cells that were CD27

^–

and a reduced frequency

cell subpopulations in pSS, RA and SLE defined by CD27

of memory B cells in patients with pSS.

expression therefore seemed to be unique.

Previous data have shown that the frequency of CD27

⁺

B

The difference between pSS and SLE (Fig. 2) is noteworthy

cells reflects the accumulation of antigen experience of an

because of the many common clinical and serologic similari-

individual that is, at least in part, related to age [73,82].

ties (hyperimmunoglobulinemia, positive anti-Ro and anti-La

autoantibodies, rheumatoid factor) between patients with

Cord blood and blood from hyper-IgM patients normally

do not contain CD27

⁺

B cells [73]. Because of the usually

pSS and those with SLE. Another difference between

patients with pSS and with SLE was the normal peripheral

more advanced age of patients with pSS than of those

B cell count in the former, whereas patients with SLE exhib-

with SLE, the actual differences identified between the

366

SLE and pSS groups might have been underestimated. In

nificant increase in the overall CD5

⁺

B cell population.

contrast, the peripheral status of B cell distributions looks

However, a subgroup of seven patients with pSS with the

very similar in patients with pSS and in those with HIV with

highest frequencies of naive B cells (86–94%) also had

predominantly naive B cells [40,80]. Because CD4

⁺

larger numbers of CD5

⁺

/CD27

^–

naive B cells

T cells are depleted in HIV but not in pSS, one interpreta-

(14.2–37.2%). In the patients analyzed, there were no

clinical features that distinguished these seven patients

tion of these observations may be that T cell dependent

with enhanced CD5

⁺

B cells from the remainder. These

priming of B cells might be less in patients with pSS than

data indicate that the previously known enhancement in

in normals and patients with SLE.

CD5

⁺

B cells in SS stems preferentially from an increase

in the immature B cell pool. It should be noted that B cells

Remarkably, the CD27

^–

B cells could be further subdi-

infiltrating the parotids frequently express CD5, further

vided by the mutational status of their productive V

_H

supporting the hypothesis of homing and activation of

rearrangements into a majority of naive cells (35 of 39 with

specific B cells in the glands.

no mutations; mutational frequency less than 0.1%) and a

minority of memory-type cells (4 of 39 with mutations;

B cell malignancies and Sjưgren’s syndrome

mutational frequency 4.6%), whereas all but one of the

CD27

⁺

B cells (31 of 32) analyzed expressed mutated IgV

In contrast to the focal sialadenitis of the minor (labial) sali-

genes [40]. Currently, the finding of the small population

vary glands, the lymphocytic lesions of the major salivary

of CD27

^–

B cells expressing mutated V

_H

rearrangements

glands often contain secondary lymph follicles. B cells

remains unclear. It is noteworthy that this population had a

have been shown to infiltrate the glandular duct epithelium

and thereby to contribute to the characteristic pattern of

significantly lower mutational frequency than CD27

⁺

chronic lymphocytic inflammation called myoepithelial

B cells (4.6% versus 7.8%; P = 0.0009). Possible expla-

nations might be transient or low-level CD27 expression,

sialadenitis (MESA) or benign lymphoepithelial lesion [90].

shedding of CD27, or stimulation that results in mutations

These lesions are thought to form the substrate for the

but fails to upregulate CD27. Notably, however, there are

development of extranodal non-Hodgkin lymphomas

no striking differences in the frequency of this population

(NHLs) [91,92]. In this context, it is well known that

between SS patients and normals [40], and, very recently,

patients with pSS have an increased risk of developing

such lymphomas compared with normals. Extranodal lym-

this population has also been detected in other normal

and abnormal conditions by studies on single cells. Impor-

phomas in pSS are almost exclusively of B cell origin and

tantly, the regulation of CD27 and its association with the

are frequently identified in the major salivary glands.

acquisition of IgV

_H

mutations seems to be normal in

Recently, the suggested linkage between autoimmunity,

autoantibody-producing cells and lymphoma [66,93,94]

patients with pSS.

has been emphasized by the demonstration of two cases

of parotid gland lymphomas in pSS producing mono-

Previous molecular analysis documented that CD27 can

specific rheumatoid factors [66].

be taken as a reliable marker for memory B cells in healthy

normals [68,74] as well as in patients with SLE [33]. The

A remarkably biased usage of individual V

_H

segments (in

analysis of a patient with SLE revealed a mutational fre-

particular the V

_H

1-69/DP-10 and V

_H

3-07/DP-54 segments)

quency of 0.4% in the CD27

^–

B cells and 6.1% in the

has been shown in both benign and malignant clonal B cell

CD27

⁺

B cells. Overall, there was no major difference in

expansions in the salivary glands of patients with pSS,

the frequency of mutations in V

_H

rearrangements of

exhibiting some evidence for (auto)antigen selection, for

CD27

^–

and CD27

⁺

B cells, respectively, obtained from

patients with pSS or SLE and from normals, which is con-

example by rheumatoid factor activity [4,58,66,95,96].

Moreover, a previous anti-idiotypic study has suggested that

sistent with the conclusion that expression of CD27 indi-

B cells expressing V

_H

1-69/DP10 cross-reactive idiotypes

cates previous antigen contact by the respective B cell.

G6, G8 and H1 are increased in infiltrates in the minor sali-

vary glands of patients with pSS [65].

Several studies have identified an enhancement of CD5-

expressing B cells in the periphery of patients with pSS

Support for a role of B cell activation in the development

[84–87], although to the best of our knowledge no study

has analyzed in detail the proportions of CD5

⁺

B cells

of lymphoma comes from phenotypic analyses of periph-

eral B cells in patients with pSS that demonstrated an

among naive and memory B cells. In contrast, a few

enhanced frequency of CD27

⁺

memory B cells in their

reports did not identify an enhanced frequency of CD5

⁺

B

cells in pSS [88]. Earlier studies [89] found enhanced fre-

peripheral blood, contrasting with patients with pSS but

no lymphoma.

quencies of CD5

⁺

B cells in about half of patients with

pSS, as well as in about half of patients with RA and

about a quarter of patients with SLE and normals. By con-

Because the expression of CD27 as well as its ligand,

trast, there was an increase only of CD5

^–

/CD27

^–

naive B

CD70, is strictly regulated on normal lymphocytes, it is

striking that neoplastic B cells at different stages of B cell

cells in patients with pSS [40], whereas there was no sig-

367

differentiation strongly express CD27 [97,98]. Notably,

on the V

_H

CDR3 and IgV

_L

chains. Overall, concentration

this included B cell malignancies with a putative origin

and maintenance of B cell activation in the salivary glands

from antigen-inexperienced B cells, such as mantle-zone

of patients with pSS leads to a significant depletion of

lymphomas [98]. In addition, a recent study reported that

memory B cells in the peripheral blood, probably resulting

7 of 10 high-grade lymphomas from HIV-positive patients

in autoantibody production and potential malignant trans-

and 6 of 10 HIV-negative patients with different lym-

formation of B lymphocytes in the glands. It will be impor-

tant to identify factors directing the migration and

phomas expressed CD27 [81]. The extent to which these

accumulation of B lymphocytes in order to interrupt the

findings indicate a loss of regulation of CD27 expression

apparent immunopathology in patients with SS.

by the malignant cells and the nature of these abnormali-

ties remain unknown. Potential explanations for the differ-

Acknowledgements

ent expression of CD27 by lymphoma might be alterations

This work was supported by Deutsche Forschungsgemeinschaft

in the circulation or stimulation of these cells as well as a

Grants Sonderforschungsbereich 421/TP C7, Do 491/4-1, 4-3 and 5-

loss of normal regulatory activity. Importantly, co-expres-