Immunohistochemistry of normal human knee synovium: a quantitative study

Abstract

Objective: To describe the immunohistochemical characteristics of knee synovium from normal healthy subjects.

Methods: 12 healthy subjects underwent needle biopsy of knee synovium. Using antibodies directed against CD3, CD4, CD8, L26, Kp-1,and HLA-DR, detailed quantitative immunohistochemical analysis of various cell subpopulations was undertaken.

Results: The mean (SD) age of the subjects was 37 (9) years (five male, seven female). All had a negative history for arthritis, no knee pain, and a totally normal joint examination except for the presence of retropatellar crepitus in five. For technical reasons staining for all immunohistochemical markers could not be achieved in all subjects. CD3+ T lymphocytes were seen in nine of 10 subjects, either diffusely or, more commonly, in perivascular areas. CD4+ cells were seen in synovium in three of seven subjects and CD8+ cells in six of eight subjects, in almost equal numbers (CD4:CD8, 1.1:1). L26+ B lymphocytes were not seen in any biopsy. Kp1+ macrophages were found in 10 of 10 subjects, predominantly in surface lining cells, and in small numbers in diffuse and perivascular locations. HLA-DR+ cells were seen in 10 of 10 subjects, predominantly in surface lining cells and diffusely, but a few were seen perivascularly.

Conclusions: Synovium from apparently normal subjects contained a wide range of different cell subpopulations but no B cells. The significance of these immune cells in normal synovium is unclear. A better understanding of their role in normal synovium may be important in analysing the transition to synovitis.

Figure 1

(A) Synovial tissue from subject 1 (no retropatellar crepitus, normal laboratory values, chlamydia negative) showing the presence of few CD3+ T cells. (B) Significant numbers of Kp1+ macrophages seen in surface lining cells and scattered cells in a diffuse distribution in the synovium of subject 2 (no retropatellar crepitus, low positive rheumatoid factor, chlamydia negative). (C) HLA-DR+ cells in the surface lining layer with a few scattered diffusely in superficial parts of synovium of subject 2. (D) Significant numbers of HLA-DR+ cells in the lining layer and in other distributions in subject 3 (no retropatellar crepitus, low positive rheumatoid factor, chlamydia negative), showing the variation in numbers of positive cells between subjects. Only nucleated cells with a distinct cytoplasmic or surface staining were counted.