Diversity of complement activation in different thyroid diseases.

Objective: To investigate complement components expression in both thyroid tissues and serum from patients with Hashimoto's thyroiditis (HT), Graves' disease (GD), and papillary thyroid cancer (PTC).

Methods: C1q, mannose binding lectin (MBL), Bb, C4d, C3d and membrane attack complex (MAC) (C5b-9) deposition and complement regulate proteins (CD46, CD55 and CD59) expression in thyroid tissues from HT, GD, PTC, and control groups were examined by IHC. C1q, MBL, Bb, C4d, C3a, and soluble C5b-9 (sC5b-9) serum levels in the HT, GD, PTC, and healthy donor (HD) groups were measured by ELISAs.

Results: MAC deposition was detected in thyroid tissues in the HT, GD and PTC groups, but not the control group. MBL, Bb, C4d, C3d and MAC staining intensities in thyroid tissues were significantly higher in the HT and PTC groups than in the control group (all P < 0.05). The C1q level was higher in HT tissues than in control tissues (both P < 0.05). No complement component had a significant difference in staining intensities between the GD and control groups. CD55 and CD59 expression levels in thyroid tissues were higher in the PTC group than in the HT, GD and control groups (all P < 0.05). Similarly, CD46 levels were higher in HT tissues than in control tissues. Bb, C4d, C3a and sC5b-9 serum levels were significantly increased in HT, GD and PTC patients compared with HDs (all P < 0.05).

Conclusion: Complement is overactivated in HT and PTC, but not in GD. All the three pathways are activated in HT, and the MBL and alternative complement pathways are activated in PTC. These distinct complement activation profiles may participate in HT, GD and PTC pathogenesis.