Anat Cell Biol.  2012 Dec;45(4):259-267. 10.5115/acb.2012.45.4.259.

Dense distribution of macrophages in flexor aspects of the hand and foot of mid-term human fetuses

• Kim JH
• Abe S
• Shibata S
• Asakawa S
• Maki H
• Murakami G
• Cho BH

• KMID: 2133911
• DOI: http://doi.org/10.5115/acb.2012.45.4.259

Abstract

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.

Keyword

CD68-positive macrophages; Hand and foot; Lymphatic vessels; Enthesis; Human fetus

MeSH Terms

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
Deoxyuracil Nucleotides
Deoxyuridine

Figure

• 

  Fig. 1 Foot and elbow of a 10-week fetus. (A, C) Hematoxylin and eosin staining, (B, D) CD68 immunohistochemistry. (B) and (D) are higher-magnification views of the squares in (A) and (C), respectively. CD68-positive macrophages are concentrated in the flexor aspects of the foot (B) and elbow (D). In the related muscles, the brachialis muscle contains particularly abundant positive cells. BR, brachioradialis muscle; C, cuneiform bones; CU, cuboid bone; FDL, tendon of the flexor digitorum longus muscle; FHL, tendon of the flexor hallucis longus muscle; MT, metatarsal bone. Scale bars=1 mm (A, C), 0.1 mm (B, D).

• 

  Fig. 2 Foot and hand of a 12-week fetus. (A, C, E) Hematoxylin and eosin staining, (B, D, F) CD68 immunohistochemistry, (G) TUNEL staining. (B, D, F) are higher-magnification views of the squares in (A, C, E), respectively. (G) corresponds to the square in (D). CD68-positive macrophages are concentrated in the flexor aspects of the foot (B, E) and hand (D). An especially high density of positive cells is evident in the loose connective tissue around the carpal tunnel (D). Stars in (D) indicate tendons of the flexor digitorum superficialis muscle. TUNEL-positive cells are seen in a tendon of the flexor digitorum profundus muscle (G). C, cuneiform bones; CU, cuboid bone; FDL, tendon of the flexor digitorum longus muscle; FHL, tendon of the flexor hallucis longus muscle; FPL, tendon of the flexor pollicis longus muscle; L, lumbricalis muscle; LPA, lateral plantar artery; MC, metacarpal bone; MT, metatarsal bone; NA, navicular; TUNEL, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling. Scale bars=1 mm (A, C, E), 0.1 mm (B, D, F). The magnification of panel G is the same as panel F.

• 

  Fig. 3 Hand of a 12-week fetus. A specimen different from that shown in Fig. 2. D2-40 immunohistochemistry for lymphatic vessels (A) and CD68 immunohistochemistry (B, C). (B) and (C) are higher-magnification views of the squares B and C in (A), respectively. In (A), podoplanin or D2-40 is positive in lymphatic vessels (arrows), a fascia on the dorsal side of the carpal tunnel (stars) and cartilages. However, these positive sites do not correspond to sites of accumulation of CD68-positive macrophages (B, C). Scale bars=0.1 mm (A-C).

• 

  Fig. 4 Hand and elbow of a 15-week fetus. (A) Hematoxylin and eosin staining, (B-F) CD68 immunohistochemistry. (B-F) are higher-magnification views of the squares B, C, D, E and F in (A), respectively. CD68-positive macrophages are concentrated in the flexor aspect of the hand (A), along the abductor pollicis brevis muscle (Abd; C), along the pronator quadratus muscle (D), in the annular ligament of the radius (E) and in the cubital fossa (F). B tendon, tendon of the biceps brachii muscle; BR, brachioradialis muscle; FDP, a tendon of the flexor digitorum profundus; MC4, fifth metacarpal bone. Scale bars=1 mm (A), 0.1 mm (B). The magnification of panel C-F are the same as panel B.

• 

  Fig. 5 Knee of a 15-week fetus and the calf of a 10-week fetus. (A-D) display a specimen different from that shown in Fig. 4, while (E) and (F) represent the same specimen as that in Fig. 1. (A, E) Hematoxylin and eosin staining, (B-D, F) CD68 immunohistochemistry. (B-D) are higher-magnification views of the squares B, C and D in (A), respectively. CD68-positive macrophages are concentrated in the flexor aspect of the knee, in contrast to the extensor aspect, where only osteoclasts are evident (C). (F) corresponding to the square in (E), shows CD68-positive macrophage accumulation in the medial, intermuscular connective tissue of the calf. MHG, tendon of the medial head of the gastrocnemius muscle; quad, quadriceps femoris (the most distal part); SM, tendon of the semimembranosus. Scale bars=1 mm (A, E), 0.1 mm (B-D, F).

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