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A monoclonal antibody OKT 9 which detects a determinant expressed by a variety of proliferating cell types has been recently developed. This antibody was used in conjunction with the immunoperoxidase technique to study the cutaneous lymphoid infiltrates of nine patients with mycosis fungoides, one patient with lymphomatoid papulosis, two patients with Sézary syndrome, and ten patients with large plaque atrophic parapsoriasis (a condition which may terminate in overt mycosis fungoides.) OKT 9 reactive cells were identified in all cases of mycosis fungoides examined, in one case of lymphomatoid papulosis, one of two cases of Sézary syndrome, and one of ten cases of large plaque atrophic parapsoriasis. These results suggest that further studies using OKT 9 should be performed to assess whether OKT 9 reactivity may be used as a prognostic marker in cutaneous lymphomas and prelymphomas.

It has been demonstrated recently in mycosis fungoides and lichen planus that T lymphocyte subsets may be identified in cutaneous lymphocytic infiltrates using the immunoperoxidase technic in conjunction with monoclonal antibodies produced by the technic of Kohler and Milstein. This communication describes the application of this technic to cutaneous lymphoid infiltrates of parapsoriasis in which T cell predominance has been demonstrated previously. The lymphoid infiltrates of six patients with atrophic parapsoriasis were examined by the indirect immunoperoxidase technic using monoclonal antibodies (from two commercial sources) directed against "helper" and "suppressor" T cell subsets. Both "helper" and "suppressor" cells (as defined by a positive reaction with monoclonal antibodies) could be identified in cutaneous infiltrates. "Helper" cells predominated, but in varying degrees among patients. The relevance of these findings in relation to the possible development of clinical mycosis fungoides from atrophic parapsoriasis is discussed. In addition, factors causing difficulty in the consistent identification of cell subtypes are discussed. These factors suggest that in the present state of imperfection, difficulty will be experienced in using this technic for the accurate quantification of percentages of lymphocyte subsets in tissue sections.U

A monoclonal antibody (OKT10), which was developed recently, reacts with pro-thymocytes, T cell acute lymphoblastic leukemia (ALL) cells, cells in normal bone marrow (including plasma cells), and activated T cells. Tissues from patients with cutaneous T cell lymphoma were studied for the presence of OKT10-reactive cells with the use of an indirect immunoperoxidase technic. OKT10-reactive cells were identified in three of eight cases of mycosis fungoides, one of two cases of Sézary syndrome, with an equivocal reaction in one of ten cases of large-plaque parapsoriasis and in one of seven positive patch tests (allergic contact dermatitis). The biologic and possible clinical implications are discussed.

The development of a monoclonal antibody directed against HLA DR (Ia-like) antigens of B cells and monocytes but not against normal peripheral human T cells suggested that this antibody might be used as a marker of B cells and monocytes in tissue sections. The T cell nature of large plaque (atrophic) parapsoriasis has recently been demonstrated by the immunoperoxidase technic. Immunoperoxidase examination of serial sections of tissues from two cases of large plaque parapsoriasis with one T cell antiserum, two monoclonal T cell antibodies, and one monoclonal reagent directed against HLA DR indicated that T cells in the cutaneous infiltrates were also HLA DR-positive. Evidence is accumulating that HLA DR positivity may be expressed by activated T cells. The findings here therefore suggest that many of the T lymphoid cells in two cases of large plaque (atrophic) parapsoriasis examined were activated in nature, and that HLA DR may not be a specific marker for B cells and monocytes in certain pathologic conditions. Caution should therefore presently be exercised in attempting to use this marker for the specific identification of B cells and monocytes in pathologic specimens, without simultaneous testing for T cell markers.

Tissues from atrophic large plaque parapsoriasis were examined using the indirect immunoperoxidase technique with a monoclonal T cell antibody as primary antibody, and affinity isolated peroxidase conjugated goat anti-mouse IgG as second stage antibody. The "T" cell nature of the dermal infiltrate and of single exocytic epidermal lymphocytes was demonstrated. The results obtained suggest that the method utilized will be useful for the demonstration of lymphoid cell subpopulations in a variety of cutaneous disorders in which a lymphocytic infiltrate forms a significant component of the histopathology observed. This technique also has the potential of providing information on the topographic localization and differentiation of lymphocytes within the various levels of the skin. Certain technical manipulations which may result in an improvement in the quality of results obtained are also discussed.

A monoclonal antibody, OKT 6, has been developed against an antigen which is expressed by immature T cells as part of their normal intrathymic differentiation, but not by mature peripheral T cells. It was though that a search for the expression of such an antigen might be worthwhile in prelymphomatous conditions. This communication describes the investigation of lymphocytic infiltrates of atropic parapsoriasis, lymphomatoid papulosis, and a small group of miscellaneous skin conditions with OKT 6 and the immunoperoxidase technic. OKT 6-positive cells were identified in the dermis in varying numbers in four cases of atrophic parapsoriasis and in one case of lymphomatoid papulosis, but not in any of the other disorders. Positive epidermal staining was noted in all tissues examined. The pattern obtained suggested that epidermal dendritic cells may react with OKT 6. The findings indicate that OKT 6-positive cells may be found outside the thymus in certain conditions. The observations in epidermis cast doubt on the exact nature of the positively reacting cells observed in dermis, suggesting that may either be immature thymocytes or possibly Langerhans cells.

"Parapsoriasis" is a term used to include a heterogeneous group of conditions, one variant of which, at least, eventuates in mycosis fungoides in a substantial percentage of cases. The T-cell origin of mycosis fungoides is well established. The lack of similar information on lymphoid cell types in parapsoriasis prompted an immunoperoxidase study using a specific antihuman T-cell serum in a group of seven patients with parapsoriasis. Our findings demonstrated a preponderantly T-cell infiltrate in the categories of parapsoriasis examined.