Lymphoid chemokine expression in Sjogren's syndrome: relationship with the lymphoid organization of the periductal inflammatory aggregates

Background

The inflammatory cellular infiltrate typical of several chronic diseases, including Sjogren syndrome (SS), is often organized in lymphoid-like structures. CXCL13 and CCL21 are lymphoid chemokines critical for physiologic development of secondary lymphoid organs. They have also been implicated in the formation of ectopic lymphoid neogenesis in various experimental and pathological conditions. To define the relationship between the in situ production of CXCL13 and CCL21 and lymphoid organization in SS we examined the expression of these chemokines in relation to the degree of B-cell and T-cell segregation, the presence of follicular dendritic cell (FDC) (CD21⁺) networks and germinal centre (GC) reactions as well as the development of high endothelial venule (HEV) (PNAd⁺)-like vessels.

Aims

The aim of this study was to characterize the organization of neolymphoid tissue in the salivary glands of SS patients and to correlate its development and maturation with the ectopic expression of lymphoid chemokines CXCL13 and CCL21

Methods

Periductal foci in 26 SS salivary gland biopsies and nine disease controls with nonspecific sialoadenitis were analysed on the base of a grading score (G1, ≤ 50 cells; G2 > 50 cells; and G3 = G2 + presence of GCs). This was related to follicular organization and maturation assessed in respect to T-cell and B-cell segregation, CD45RO and CD45RA expression (CD3⁺, CD20⁺ and UCH10, S130), FDC networks (CD21⁺) and PNAd (MECA-79+) HEV formation and CXCL13 and CCL21 expression.

Results

In SS samples, G1 aggregates showed preponderance of CD3⁺/CD45RO⁺ infiltrating lymphocytes without B/T area segregation, G2 revealed an increasing number of CD20⁺/CD54RA⁺ and a variable degree of organization (54.55% not segregated, 21.21% atypically segregated, 24.24% segregated), while G3 exhibited CD20⁺/ CD54RA⁺ majority with the typical segregation of secondary lymphoid follicles. Within G2 and G3 aggregates we identified CD21⁺ cells clusterized or in a reticular pattern within the GCs. MECA79⁺ vessels were detected on the edge of the aggregates. CXCL13 expression was seen in 4.07% of G1, 46.16% of G2 and 100% of G3 lymphocytic aggregates. CXCL13 was localized within G2 aggregates, in G3 inside CD21⁺ GCs and in some infiltrated ducts. CCL21 expression was detected in 2.5% of G1, 17.85% of G2 and 47.62% of G3 aggregates. CCL21 was related with the endothelium of HEV morphology structures and some cells surrounding these structures. In nonspecific sialoadenitis samples we detect no follicle formation or features of secondary lymphoid organ formation.

Conclusions

In the salivary gland of patients with SS a true phenomenon of lymphoneogenesis appears to take place, characterized by the formation of mature follicles with GCs, B/T segregation, FDC networks and PNAd expression on HEVs.

CXCL13 and CCL21 expression clearly correlates with the higher grades of organization of the infiltrates. The presence of lymphoid structures within the target organs for the disease and the association of these structure with chemokines acting as regulators of lymphoneo-genesis in secondary lymphoid organs, combined with the possible expression of CXCL13 even in the absence of professional FDCs, suggests a key role for these molecules in the pathogenesis, maintenance and evolution of the disease process.