M. Ono et al.

the other antibodies. It is reported that thestructure of guinea pig IGF-1 is similar tothat of human IGF-1 (LeRoith et al., 1993).
In this study, we used anti-human IGF-1
antibody and anti-human IGF-1 receptor
antibody for detection of IGF-1 and IGF-1
receptor of guinea pig.

AResults
Based on the histological-histochemical
grading system, five 1- to 5-month-old animals were classified as the mild group. The
mean osteoarthritis grade was 0.60 ± 0.89.
Seven 3- to 8-month-old animals were included in the moderate group, with a meanosteoarthritis grade of 5.14 ± 1.77. Five 8to 18-month-old animals comprised the severe group, with a mean osteoarthritis
grade of 9.40 ± 0.89.

TB

M

Histopathological findings
Mild group (grades 0–2)
When articular cartilage of the medialcondyle of the tibia in the mild group wasexamined, fibrous connective tissue continuous with the synovial membrane andcovering the margins of the articular cartilage was observed at the synovium-cartilage junction in all animals. Fibrous connective tissue at this junction was not stained with safranin O. In the most superficial
layer of the fibrous connective tissue at thejunction, fibroblastic-like cells were present almost continuously from superficial
cells of the synovial membrane. In a layer
deeper than these fibroblastic-like cells,chondrocytes were observed, but thesewere not clustered. Osteophyte formation
was not noted in any animal (Fig. 1A).
In the weight-bearing regions of the cartilage of animals showing osteoarthritis
changes, a rougher structure of the superficial layer, slight proliferation of chondrocytes, and slightly decreased safranin-Ostaining intensity were noted.

CFig. 2. Chondrocytes (arrowheads) cluster in a layer deeper than fibroblastic-like cells in the fibrous connective tissue (arrows) in the moderate group of 3-month-old animals, in which degenerative changes had progressed further (A, B). These chondrocytes, which are negative for
type-I and -III collagens and PCNA in the mild group, arepositive for all (B, D, E respectively) in the moderategroup. This staining pattern is similar to that of fibroblastic-like cells in the fibrous connective tissue. Aroundthese chondrocytes, cartilage matrix positive for type-II
collagen is recognized (C). IGF-1 (F) and IGF-1 receptor(G) are identified in fibroblastic-like cells and chondrocytes seen in a layer deeper than the fibroblastic-like cells.
M, medial meniscus; T, tibia. Original magnification, ×200.
[Figs. 2A–C on p. 134; Figs. 2D–G on p. 135]134

Processes of osteophyte formation

Moderate group (grades 3–7)
In the moderate group in which cartilage degeneration had progressed further,cells similar to chondrocytes had clusteredin a layer below fibroblastic-like cells near
the superficial layer of the margins of thearticular cartilage. These cells had lesscytoplasm. Chondrophyte formation wasnoted in 1 animal and osteophyte formationin another (Fig. 2A).
The weight-bearing regions of the cartilage showed fissures extending to the transitional zone and moderate to marked reduction in safranin-O staining intensity.
The number of chondrocytes was decreased.

DE

Severe group (grades 8–13)
A chondrophyte was identified in 1 animal (Fig. 3A) and osteophytes in 4 animals. Fibrous connective tissue of thesynovium-cartilage junction and fibroblastic-like cells were noted around theosteophyte. Chondrocytes were recognized near the boundary between the osteophyte and weight-bearing regions of thecartilage, but had not clustered (Fig. 4A).
Fissures from the radial zone to the calcified zone and markedly reduced safraninO staining intensity were noted in the weightbearing regions of the cartilage. The number of chondrocytes was noticeably decreased.

FSynovial membrane
The lining cells of the synovium consisted of 2 to 4 layers and proliferated morewith osteoarthritis progression, but there
were no findings suggestive of synovitis,such as villous formation or cell infiltration
into sublining synovial tissue.

GImmunohistological staining
Mild group
At the margins of the articular cartilage,
the cytoplasm of fibroblastic-like cells in
the fibrous connective tissue was positive
for type-I (Fig. 1B) and -III (Fig. 1D) col

Figs. 2D–G. Continued from the previous page.

135