Table 1 Selected articles on immunohistochemical localization of inflammatory cells in idiopathic inflammatory myopathies

T lymphocytes

[9]

53 patients. T lymphocytes were least abundant at perivascular and most abundant at endomysial sites. The CD4/CD8 ratio was highest at perivascular sites and lowest at endomysial sites. The proportion of T lymphocytes estimated to be Ia⁺, or activated, was nearly twice as high at endomysial sites as at perivascular sites

31 patients. The proportion of T lymphocytes was lowest at perivascular sites and highest at endomysial sites. The CD4/CD8 ratio was highest at perivascular sites and lowest at endomysial sites. Many inflammatory cells display the Ia marker, but only one-sixth of perivascular lymphocytes and one-fifth of endomysial T lymphocytes was Ia⁺, or activated

48 patients. T lymphocytes were least abundant at perivascular sites and most abundant at endomysial sites. CD4/CD8 ratio was highest at perivascular sites and lowest at endomysial sites. The proportion of T lymphocytes estimated to be Ia⁺, or activated, was nearly twice as high at endomysial sites as at perivascular sites

[8]

7 patients. Endomysial infiltrates of T lymphocytes were predominant. Partly invaded non-necrotic cells were also seen; some of these fibers also expressed MHC class I

21 patients. Severe muscle fiber necrosis, predominant perivascular T lymphocyte infiltrates, fibrosis and perifascicular atrophy. MHC class I were localized to perifascicular fibers

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[11]

5 patients. Perforin was co-localized with granzyme A and occasionally invaded non-necrotic muscle fibers. The percentage of perforin⁺ cells among the endomysial CD8⁺ cell population was 9.9%

5 patients. There were very few perforin⁺ and granzyme A-positive cells in DM

2 patients. Perforin was co-localized with granzyme A and occasionally invaded non-necrotic muscle fibers. The percentage of perforin⁺ cells among the endomysial CD8⁺ cell population was 12.5%

[10]

5 patients. Co-localization of perforin with CD8, CD4, CD3, and CD2 was analyzed. The general distribution of inflammatory cells was endomysial. The overall CD4/CD8 ratio was 1.1 and the total number of CD8⁺ inflammatory cells in 9 random microscopic fields was 236. More than 90% of perforin⁺ cells were CD2⁺CD3⁺, and perforin was expressed both in non-invasive interstitial T lymphocytes and in autoinvasive CD8⁺ T lymphocytes. Of all perforin⁺ cells, 60% were CD8⁺ and 40% CD4⁺. Conversely, 75% of the CD8⁺ cells and 50% of the CD4⁺ cells were perforin⁺. 43% of the CD8⁺ T lymphocytes that contacted a muscle fiber expressed perforin vectorially toward the target muscle fiber

4 patients. Co-localization of perforin with CD8, CD4, CD3, and CD2 was analyzed. The general distribution of inflammatory cells was perivascular and perimysial. The overall CD4/CD8 ratio was 1.2 and the total number of CD8⁺ inflammatory cells in 9 random microscopic fields was 167. More than 90% of perforin⁺ cells were CD2⁺CD3⁺, and 50% of all perforin⁺ cells were CD4⁺ and 50% were CD8⁺. Conversely, 80% of the CD4⁺ cells and 90% of the CD8⁺ cells were perforin⁺. Perforin was distributed randomly in the cytoplasm of the inflammatory T lymphocytes

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[13]

17 patients. The numbers of CD4, CD8, and CD56 cells per 1,000 muscle fibers at endomysial sites were 275 ± 140, 355 ± 150, and 25 ± 13 (means ± SD) in all cases. Granulysin was expressed in the cytoplasm of infiltrating cells, mostly CD4⁺ and CD8⁺ cells, only a few CD56⁺ cells at a higher level in endomysial sites than in perivascular sites. Notably, steroid-resistant patients with PM had a higher frequency of double-positive CD8 and granulysin at endomysial sites than steroid-resistant patients with IBM

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7 patients. The numbers of CD4, CD8, and CD56 cells per 1,000 muscle fibers at endomysial sites were 250 ± 120, 330 ± 200, and 31 ± 16 (means ± SD) in all cases. Granulysin was expressed in the cytoplasm of infiltrating cells, mostly CD4 and CD8⁺ cells, only a few CD56⁺ cells at a higher level at endomysial sites than at perivascular sites

[61]

2 patients. CD8⁺ T lymphocytes were found to invade muscle fibers co-expressing ICOS-L and MHC class I. The endomysial ICOS-positive CD8⁺ and CD4⁺ T lymphocytes were seen at a similar frequency and ratio to those in patients with IBM

2 patients. Most ICOS and ICOS-L positive cells were localized to the perimysial regions and connective tissue. ICOS-expressing CD4⁺ and CD8⁺ T lymphocytes were infrequent and present only in the perimysium and around blood vessels, but not among autoinvasive T lymphocytes

20 patients. CD8⁺ T lymphocytes were found to invade ICOS-L and MHC class I co-expressing muscle fibers. ICOS-L expression was found on the surface of almost all fibers, including healthy myofibers away from inflammation. 1/20 or 2/20 autoinvasive CD8⁺ T lymphocytes were double- positive for ICOS and CD8. A similar percentage of CD4⁺ T lymphocytes, partly found in close contact with CD8⁺ T lymphocytes, also showed ICOS double immunoreactivity

B lymphocytes

[9]

53 patients. B lymphocytes were most abundant at perivascular sites and least abundant at endomysial sites; however, only few B lymphocytes were expressed in comparison with patients with dermatomyositis

31 patients. B lymphocytes were most abundant at perivascular sites and least abundant at endomysial sites

48 patients. B lymphocytes were most abundant at perivascular sites and least abundant at endomysial sites; however, only few B lymphocytes were expressed compared with dermatomyositis

Polymyositis, dermatomyositis, and inclusion-body myositis, [34]; dermatomyositis, [49]

3 patients. Occasional scattered B lymphocytes (CD19 and CD20) with a mean density of 2.8 cells/mm² were seen. Plasma cells (CD138) showed a mean density of 11.0 cells/mm². CD138⁺ cells were located predominantly in the endomysium. There were 3.9-fold more plasma cells than B lymphocytes

No data were given for 5 patients with dermatomyositis who were investigated for B lymphocytes (CD19 and CD20) and plasma cells (CD138). However, a comparison was done with another study in which it was shown that IBM muscle tissue had 0.84-fold B lymphocytes and 4.3-fold plasma cells

16 patients. Occasional scattered B lymphocytes (CD19 and CD20) with a mean density of 4.2 cells/mm² were seen. Plasma cells (CD138) showed a mean density of 17.2 cells/mm². CD138⁺ cells were located predominantly in the endomysium. There were 4.1-fold more plasma cells than B lymphocytes

Dendritic cells

Polymyositis and inclusion- body myositis, [48]; dermatomyositis, [49]

10 patients. Collections of myeloid DCs (BDCA-1⁺) were present in 90%, widely distributed across the section with additional high-density accumulations. High-density accumulations were typically endomysial and either surrounded myofibers and sometimes invaded apparently non-necrotic myofibers. They were also expressed in dense collections of cells (always some CD3⁺ cells in these dense collections) between myofibers. Hardly any plasmacytoid DCs (BDCA-2⁺) were seen

14 patients. Plasmacytoid DCs (BDCA-2⁺) were seen in 10/14 patients and were mainly localized to endomysial and preivascular locations

20 patients with IBM were investigated. Collections of myeloid DCs (BDCA-1⁺) were present in 17/20 patients widely distributed across the section with additional high-density accumulations. These high- density accumulations were typically endomysial and either surrounded myofibers and sometimes invaded apparently non-necrotic myofibers. They could also be expressed in dense collections of cells (always some CD3⁺ cells in these dense collections) between myofibers. Hardly any plasmacytoid DCs (BDCA-2⁺) were seen

Dermatomyositis, [49]; inclusion-body myositis, [48,49]

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14 patients. MxA was expressed in perifascicular areas. Eight patients showed MxA expression by myofibers in a preferentially perifascular distribution in both atrophic and normal-sized fibers but also in capillaries and other blood vessels in 13/14 patients. In regions of perifascicular atrophy all myofibers were positive

20 patients. A quantitative study has been done between patients with IBM and DM who had not received immunosuppressive treatment. The numbers of myeloid and plasmacytoid DCs were similar in perivascular and perimysial areas in IBM. However, the endomysial locations of myeloid DC numbers were a mean of 3-fold higher than those of plasmacytoid DCs. In contrast, in DM there were 16-fold and 3-fold more plasmacytoid DCs than myeloid DCs in endomysial and perivascular sites, respectively

[47]

6 patients. Immature DCs (CD1a) were mainly found in lymphocytic infiltrates in all patients. Mature DCs (DC-LAMP/CD83) were localized to perivascular infiltrates surrounding muscle fibers

6 patients. Immature DCs (CD1a) were mainly found in lymphocytic infiltrates in all patients. Mature DCs (DC-LAMP/CD83) were localized to perivascular infiltrates surrounding muscle fibers

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