In the developing human musculoskeletal system, cell death with macrophage accumulation occurs in the thigh muscle and interdigital area. To comprehensively clarify the distribution of macrophages, we immunohistochemically examined 16 pairs of upper and lower extremities without the hip joint (left and right sides) obtained from 8 human fetuses at approximately 10-15 weeks of gestation. Rather than in muscles, CD68-positive macrophages were densely distributed in loose connective tissues of the flexor aspects of the extremities, especially in the wrist, hand and foot. In contrast, no or fewer macrophages were evident in the shoulder and the extensor aspects of the extremities. The macrophages were not concentrated at the enthesis of the tendon and ligament, but tended to be arranged along other connective tissue fibers. Deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling revealed apoptosis in the hand lumbricalis muscles, but not in the area of macrophage accumulation. Likewise, podoplanin-positive lymphatic vessels were not localized to areas of macrophage accumulation. Re-organization of the connective tissue along and around the flexor tendons of the hand and foot, such as development of the bursa or tendon sheath at 10-15 weeks, might require the phagocytotic function of macrophages, although details of the mechanism remain unknown.
Apoptosis ; Cell Death ; Connective Tissue ; Deoxyuracil Nucleotides ; Deoxyuridine ; Extremities ; Fetus ; Foot ; Hand ; Hip Joint ; Humans ; Ligaments ; Lower Extremity ; Lymphatic Vessels ; Macrophages ; Muscles ; Musculoskeletal System ; Pregnancy ; Shoulder ; Tendons ; Thigh ; Wrist

Background: Comparative analysis of virulence factors (VFs) between Pasteurella canis and Pasteurella multocida are lacking, although both cause zoonotic infections. We determined the virulence-associated genome sequence characteristics of P. canis and assessed the toxin gene prevalence unique to P. canis among clinical isolates of P. canis and P. multocida. Methods: We selected 10 P. canis and 16 P. multocida whole-genome sequences (WGSs) from the National Center for Biotechnology database. The VFanalyzer tool was used to estimate P. canis-characteristic VFs. Amino acid sequences of VFs were compared with multiple-aligned sequences. The genome structure containing P. canis-characteristic and adjacent loci was compared to the corresponding P. multocida genome structure. After designing primer sequences and assessing their accuracy, we examined the gene prevalence of the P. canis-characteristic VFs using PCR among clinical isolates of P. multocida and P. canis. Results: Using VFanalyzer, we found virulence-associated cytolethal distending toxin (cdt)A–cdtB–cdtC loci common to all P. canis WGSs that were not found in P. multocida WGSs. Similarities in the multiple alignments of CdtA–CdtB–CdtC amino acid sequences were found among the 10 P. canis WGSs. Shared or similar loci around cdtA–cdtB–cdtC were identified between the P. canis and P. multocida genome structures. The PCR-based cdtA–cdtB–cdtC prevalence differed for P. canis and P. multocida clinical isolates. Conclusions P. canis-specific cdtA–cdtB–cdtC prevalence was identified among clinical isolates. These three loci may be unique toxin genes and promising targets for the rapid identification of P. canis in clinical settings.