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Polymyositis (PM) and dermatomyositis (DM) are the prototypical inflammatory diseases of skeletal muscle. In PM, CD8 ϩ T cells invade and destroy muscle fibers, whereas humoral effector mechanisms prevail in DM. We studied the expression of the cytotoxic mediator perforin in inflammatory cells in PM and DM muscle by semiquantitative PCR, immunohistochemistry and confocal laser microscopy. Similar levels of perforin mRNA were expressed in PM and DM, and abundant perforin-expressing CD3 ϩ CD8 ϩ and CD3 ϩ CD4 ϩ T cells were observed in both diseases. However, there was a striking difference in the intracellular localization of perforin. In DM, perforin was distributed randomly in the cytoplasm of the inflammatory T cells. In contrast, 43% of the CD8 ϩ T cells that contacted a muscle fiber in PM showed perforin located vectorially towards the target muscle fiber. The results suggest ( a ) that the random distribution of perforin in the cytoplasm of muscle-infiltrating T cells observed in DM reflects nonspecific activation, and ( b ) that the vectorial orientation observed only in PM reflects the specific recognition via the T cell receptor of an antigen on the muscle fiber surface, pointing to a perforin-and secretion-dependent mechanism of muscle fiber injury. ( J. Clin. Invest. 1996. 97:2905-2910.)

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SUMMARYWith the advent of standard flow cytometric methods using two-colour fluorescence on satnpies of whole blood, it is possible to establish the ranges of CD3, CD4 and CD8 T lymphocyte subsets in the routine laboratory, and also to assist the definition of HIV-l-re!ated deviations from these normal values. In 676 HIV-I-seronegative individuals the lymphocyte subset percentages and absolute counts were determined. The samples taken mostly in the morning. The groups included heterosexual controls, people with various clotting disorders but without lymphocyte abnormalities as well as seronegative homosexual men as the appropriate controls for the HIV-I-infected groups. The stability of CD4"/ values was demonstrated throughout life, and in children CD4 values <25% could be regarded as abnormal. The absolute counts ofall Tcell subsetsdeereased from birth until the age of ID years. In adolescents and adults the absolute numbers {mean±s.d.) of lymphocytes, CD3. CD4 and CD8 eells were I 90 + 0-55. I 45 + 046. 083+029 and 056 + 0 23 X iO'*//, respectively. In patients with haemophilia A and B the mean values did not differ signifieantly. In homosexual men higher CD8 levels were seen compared with heterosexual men and 27"/;. had an inverted CD4/CD8 ratio but mostly without CD4 lymphopenia {CD4<04x 107/), However, some healthy uninfected people were 'physiologieally' lymphopenic without having inverted CD4/CD8 ratios. When the variations "within persons" were studied longitudinally over a 5-year period, the absolute CD4 counts tended to be fixed al different levels. As a marked contrast, over 60% of asymptomatic HIV-I ' patients exhibited low CD4 counts <04x 10"//together with inverted CD4/CD8 ratios. Such combined changes among the heterosexual and HIV-1-seronegative homosexual groups were as rare as 14% and 3%. respectively. For this reason, when the lymphoeyte tests show < 0-4 X IO**// CD4 eount and a CD4/CD8 ratio ofless than unity, the individuals need to be investigated further for ehronicity of this disorder, the signs of viral infections sueh as HIV-I and other eauses of immunodeficiency.