Immunolocalization of Collagens (I and III) and Cartilage Oligomeric Matrix Protein in the Normal and Injured Equine Superficial Digital Flexor Tendon

Figures & data

Table 1. The regions of different structural appearances in the individual tendons, displayed as percentage of total section area

ID	Breed	Limb	Age	Duration of injury	Normal aligned (%)	Endotenon (%)	Fibroblastic organized (%)	Fibroblastic disorganized (%)	Necrosis (%)	Hemorrhage (%)
A	SWB	Left	7	3 weeks	5	10	5	20	45	15
B	SWB	Left	7	MD	5	0	30	60	5	0
C*	SWB	Left	8	>3 months	0	5	80	10	5	0
D*	SWB	Right	8	>3 months	0	5	70	20	5	0
E	SWB	Left	13	>1 year	25	5	20	5	45	0
F	TB	Left	5	MD	80	10	5	0	5	0
G	TB	Right	25	>6 months	20	5	65	5	5	0
H*	STB	Left	5	>1 year	5	10	30	50	5	0
I*	STB	Right	5	>1 year	5	10	60	25	0	0
K	TB	Right	13	–	95	5	0	0	0	0
L	TB	Left	3	–	95	5	0	0	0	0
M	TB	Left	3	–	95	5	0	0	0	0

Notes: The data are calculated at the light microscopic level on H&E-stained slides from the mid-metacarpal region of the superficial digital flexor tendon. SWB, Swedish Warmblood (show jumpers); TB, Thoroughbred horse; STB, Standardbred Trotter; MD, missing data.

*C, D, H, and I are right and left tendons from two horses.

Table 2. The labeling of COMP and type I and III collagens is displayed in the different regions of the tendon in each individual, as immunopositive staining, graded as 0, 1, 2, and 3, where 0 represents no staining and 3 represents a marked staining

	Normal aligned				Endotenon				Fibroblastic organized				Fibroblastic disorganized				Necrosis
	COMP	COMP	Type I collagen	Type III collagen	COMP	COMP	Type I collagen	Type III collagen	COMP	COMP	Type I collagen	Type III collagen	COMP	COMP	Type I collagen	Type III collagen	COMP	Type I collagen	Type III collagen
ID	Immuno	In Situ	Immuno	Immuno	Immuno	In Situ	Immuno	Immuno	Immuno	In Situ	Immuno	Immuno	Immuno	In Situ	Immuno	Immuno	Immuno	Immuno	Immuno
A	2	0	3	ND	2	ND	3	2	0	3	1	1	2	1	3	3	1	3	3
B	2	3	3	3	2	ND	3	2	ND	ND	ND	ND	2	2	3	1	2	3	3
C	ND	ND	3	ND	2	3	3	1	0	0	1	1	2	3	3	3	ND	ND	ND
D	ND	ND	ND	ND	2	3	3	2	0	0	1	1	2	1	3	3	1	ND	3
E	1	2	2	2	1	2	1	1	0	1	1	2	1	1	1	ND	0	1	1
F	2	3	2	0	1	ND	2	1	0	2	1	2	1	ND	ND	ND	1	2	0
H	2	3	3	3	2	3	3	2	0	0	0	1	2	3	3	2	2	3	2
G	1	2	2	0	1	3	3	1	1	1	1	2	1	ND	2	1	1	3	0
I	3	3	3	2	1	2	3	1	0	0	0	1	1	1	2	2	ND	ND	ND
K	3	2	3	0	ND		ND	ND	0	0	0	3	ND		ND	ND	ND	ND	ND
L	3	2	3	0	ND		ND	ND	0	0	0	3	ND		ND	ND	ND	ND	ND
M	3	2	3	0	ND		ND	ND	0	0	0	3	ND		ND	ND	ND	ND	ND

Notes: The expression of COMP mRNA (in situ) is also presented as nonpositive cells (0) and a majority of cells were positive (3). ND, the structure is not detected in the section; SWB, Swedish Warmblood (show jumpers); TB, Thoroughbred; STB, Standardbred Trotter.

Figure 1.  Microscopic longitudinal section (H&E stained) of a normal tendon (L). Note the aligned fiber bundles with tenocytes in parallel rows and thin endotenon (arrows). L refers to tendon ID (see Tables 1 and 2). Bar = 100 μm.

Figure 2. Microscopic longitudinal section (H&E stained) of an injured tendon (C) displaying an organized fibroblastic region. There is a high cellularity with fibroblastic cells and fibers in longitudinal parallel arrangement. Vessels are present between fibers (arrows). C refers to tendon ID (see Tables 1 and 2). Bar = 200 μm.

Figure 3. Microscopic longitudinal section (H&E stained) of an injured tendon (H) showing a disorganized region with high amount of fibroblastic cells (arrows) and many vessel-like structures (arrowheads) compatible with neovascularization. H refers to tendon ID (see Tables 1 and 2). Bar = 100 μm.

Figure 4. Microscopic longitudinal section (H&E stained) of injured tendon (A) characterized by acellular necrotic area (arrows) and hemorrhages (*). A refers to tendon ID (see Tables 1 and 2). Bar = 100 μm.

Figure 5. Microscopic longitudinal section of a normal tendon (K). Immunohistochemical localization of COMP. Note the staining in the normally aligned fibers. K refers to tendon ID (see Tables 1 and 2). Bar = 100 μm.

Figure 6. Microscopic longitudinal section of an injured tendon (C). A: Immunohistochemical localization of COMP in a fibroblastic organized region with a marked staining (arrows) and in endotenon (arrowheads). Bar = 100 μm. B: In situ hybridization with the expression of COMP m-RNA (dark stain) in the cytoplasm of the majority of cells (arrows) in the same region as a). C refers to tendon ID (see Tables 1 and 2). Bar = 100 μm.

Figure 7. Microscopic longitudinal section of injured tendon (H). Immunohistochemical localization of type I collagen. Note the intense staining of the organized fibroblastic tissue, but lack of staining in the extensive endotenon (arrows). H refers to tendon ID (see Tables 1 and 2). Bar = 100 μm.

Figure 8. Microscopic longitudinal section of a normal tendon from a control (K). Immunohistochemical localization of type III collagen. A marked immunostaining is present in the endotenon (arrows), but the aligned fibers do not show any staining. K refers to tendon ID (see Tables 1 and 2). Bar = 100 μm.

Figure 9. Microscopic longitudinal section of an injured tendon (B). Immunohistochemical localization of type III collagen. A marked immunostaining is present in an atypical, disorganized region. B refers to tendon ID (see Tables 1 and 2). Bar = 100 μm.