Porphyromonas gingivalis FimA fimbriae: Roles of the fim gene cluster in the fimbrial assembly and antigenic heterogeneity among fimA genotypes

In order for bacteria to exert their pathogenicity, they must adhere to and colonize the host tissues. Porphyromonas gingivalis, a periodontal pathogen, primarily exploits FimA fimbriae for adhesion and colonization. FimA fimbriae are polymers composed of FimA protein encoded by the fimA gene. The fimA gene exists as a single copy within the fim gene cluster. This fim gene cluster contains 7 genes: fimX, pgmA, and fimABCDE. In this article, we address the roles of these genes in fimbrial formation. P. gingivalis strains 381 and ATCC 33277 express long fimbriae several micrometers in length, but we found that the FimB protein is absent in these strains because of a nonsense mutation in the fimB gene. Moreover, we found that FimB restoration resulted in the production of short FimA fimbriae approximately 150 nm in length. These findings indicate that FimB regulates fimbrial length. We also demonstrate that genes in the fim gene cluster, except fimA, are not required for FimA fimbrial assembly. It has been reported that there are several fimA genotypes, and these are associated with differential virulence. As such, we describe a serological analysis of FimA fimbriae across genotypes. We obtained antisera elicited by FimA fimbriae from genotypes I to V. The antisera showed low cross-reactivity between genotypes, indicating that the FimA fimbriae of each genotype were antigenically heterogenic. In addition, the antisera preferentially recognized the polymeric conformation of the fimbriae, which may be responsible for the heterogeneity. Notably, however, the amino acid sequences are partially common among each genotype.     

OSTEOSARCOMA AS A SECOND MALIGNANCY AFTER TREATMENT FOR NEUROBLASTOMA

A 4-month old girl was diagnosed as having stage IV neuroblastoma of the right adrenal gland. Preoperative chemotherapy was given, followed by local surgical excision. Postoperatively, irradiation of the tumor bed and adjuvant chemotherapy was given for 11 months. Nine years after cessation of chemotherapy, the patient developed left hip-joint pain. Biopsy of the ischium showed chondroblastic osteosarcoma. Limb salvage surgery was performed after preoperative chemotherapy. Postoperatively, adjuvant chemotherapy was given for 14 months. Twenty-two months after treatment for the secondary osteosarcoma, the patient has been remained in disease-free condition without any evidence of relapse. A second osteosarcoma occurring outside the radiation field after treatment for neuroblastoma is quite rare. This unusual case emphasized the need for close monitoring for development of second malignant neoplasms in survivors of neuroblastoma even in the absence of a known predisposing factor, such as radiation therapy.     

High calcium enhances the expression of double‐stranded RNA sensors and antiviral activity in epidermal keratinocytes

Double‐stranded RNA (dsRNA) sensors including TLR3, MDA5 and RIG‐I are expressed in epidermal keratinocytes and play an important immunological role by enhancing various innate and adaptive immune responses. Although the role of elevated extracellular calcium concentration in keratinocyte differentiation is well understood, the effect of high calcium on dsRNA sensors is not well studied. We investigated alterations in dsRNA sensor expression and antiviral activity induced by a high extracellular concentration of calcium in epidermal keratinocytes. Normal human epidermal keratinocytes (NHEKs) were stimulated with high calcium and/or synthetic dsRNA, poly (I:C). TLR3, IFIH1 (MDA5) and DDX58 (RIG‐I) expression were measured via qPCR, and IFN‐β and human beta‐defensin 2 (HBD2) levels were measured using ELISA. TLR3 localization was evaluated with immunocytofluorescence. Antiviral activity was quantified with virus plaque assays using herpes simplex virus type 1 (HSV‐1). High calcium significantly upregulated mRNA expression of TLR3, IFIH1 and DDX58 in NHEKs. In addition, high calcium significantly enhanced poly (I:C)‐induced anti‐HSV‐1 activity in NHEKs. The antiviral molecule HBD2 but not IFN‐β induction by poly (I:C) was enhanced by high calcium. Our findings indicate that high levels of extracellular calcium enhance the expression of dsRNA sensors and augment antiviral activity in epidermal keratinocytes.