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psi-3 is a monoclonal antibody that recognizes a 135,000 molecular weight structural component of maturing keratinocytes in psoriasis (the psi-3 antigen) but fails to bind to any constituent of keratinocytes in normal epidermis. This paper describes the occurrence of the psi-3 antigen in a variety of dermatopathologic conditions using immunoperoxidase (biotin-avidin-peroxidase) and immunofluorescence methods which show excellent concordance. In 35 of 36 specimens of psoriasis vulgaris, psi-3 antibody consistently immunolabels the cytoplasm of keratinocytes above the basal layer. At the edges of psoriatic plaques, psi-3 antibody staining extends for a variable distance into lesion-free epidermis. A similar pattern has been found in a certain number of other conditions described in the paper, including squamous cell carcinoma and condyloma acuminatum, but not Darier's disease, basal cell carcinoma, nor lamellar ichthyosis. In all but one condition, the outermost or basal layer of cells is never stained. The only disease in which the lowermost cell layer is stained is a lichen planus-like lesion. The occurrence of psi-3 antigen cannot be correlated with any histologic feature of psoriasis such as acanthosis, loss of the granular layer, or hyperproliferation. The antigen appears to be a unique keratinocyte constituent which is expressed in certain pathologic conditions and which is not detected by any other histologic or immunophenotyping method. It is a potentially valuable addition to the panel of antibodies available for characterizing epithelial cells.

The potential therapeutic value of anti-idiotypic antibodies during B cell proliferations largely depends on the stability of the target Ig idiotopes. We investigated this stability in a clinical condition of so called nonmalignant monoclonal B cell proliferation, mixed cryoglobulinemia. The idiotypic profile of a single IgM kappa monoclonal auto-antibody with anti-IgG activity (rheumatoid factor (RF] which originated from a patient suffering from a nonmalignant mixed cryoglobulinemia was followed over a period of 3 yr. As judged from the reactivity of a panel of five different mouse monoclonal anti-idiotypic antibodies mapping the RF variable regions, there was no idiotypic change in the serum IgM RF. At a cellular level, in vitro stimulation of the patient's PBL gives rise to IgM kappa auto-antibodies that were shown to bear the same idiotypic determinants as the serum IgM kappa. We then investigated the effects of the anti-idiotypic antibodies on the in vitro IgM kappa production. When stimulated with PWM and in the presence of anti-idiotypic antibodies (10 micrograms/ml), the patient's PBL produced less IgM RF (18 to 62% inhibition). The same inhibition of IgM RF production was observed after EBV infection of the patient's PBL (from 19 to 90% inhibition). In both cases, the remaining IgM RF production was idiotypically indistinguishable from the serum IgM RF. The implications of the idiotypic stability and of the results of in vitro idiotypic manipulation could be important in view of both the understanding of nonmalignant cryoglobulinemia and of the possible therapeutic use of anti-idiotypic antibodies in diseases.

In an effort to analyze both IgM rheumatoid factor (RF) repertoire and regulation of RF production in humans, we developed a panel of four mouse monoclonal antibodies (mAb) defining distinct K light chain-associated idiotopes (id) of a human monoclonal IgM RF (Alt). These mAb (A75, AM1, AM2, AM3) had equivalent reactivities with the immunizing RF during classic inhibition of antigen-binding assays. These anti-id reagents were reacting to neither other tested monoclonal IgM RF nor normal polyclonal IgM. It was possible to distinguish the id defined by the mAb from the results of four sets of experiments: dissociation of Alt RF heavy (H) and light (L) chains showed that A75, AM1, and AM2 reacted to id located on the L chain, whereas AM3 defined a conformational RF id; recombination experiments of H and L chains showed that A75 and AM2 reacted well with both homologous (Alt H + Alt L) and heterologous (Alt L + unrelated H) recombinants, whereas AM1 reacted better with the homologous recombinant than with the heterologous one; the relative affinities of the mAb were drawn from their ability to shift already bound labeled Alt RF from solid phase IgG; and radiolabeling of two mAb (A75 and AM3) and experiments of inhibition of id binding with cold anti-id and cold anti-CK showed that A75 recognized a proximal id (close to the K constant region), whereas AM3 defined a more distal id, AM2 and AM1 being located between A75- and AM3-defined sites. This topographic mapping of K light chain-associated id of a human RF with anti-id of known relative affinities could help in studying idiotypic regulation in humans.

We have compared the staining patterns of Ulex europeus agglutinin (UEA) I-FITC and Helix pomatia agglutinin (HPA)-FITC on normal and psoriatic epidermis in order to follow the production of the binding sites as a function of maturation. We have further characterized them with respect to solvent extraction and enzyme digestion. The bandlike pattern of membrane staining by UEA I in the upper spinous and granular layer cells of normal epidermis is lost in psoriasis. Instead there is a fainter cytoplasmic staining which is largely sensitive to chloroform/methanol extraction, and thus presumably is glycolipid in nature. Epidermal binding of HPA to normal skin sections is mainly seen in cell membranes. It spares the basal layer and then increases from the suprabasal region to the granular layer. HPA staining in the spinous layer is destroyed by extraction with Triton X-100. In contrast, binding to the membranes of cells in psoriatic epidermis is triton-resistant. The result indicates the production of a component early in the maturation pathway which has no counterpart in normal skin. HPA binding to the spinous cells of symptomless skin from psoriatic patients shows decreased sensitivity to Triton X-100 by comparison with normal. The results are discussed in terms of changes in the pathway of keratinocyte maturation in psoriasis.

We have isolated a murine monoclonal antibody, called psi-3, which immunolabels maturing keratinocytes in psoriatic skin but not in normal epidermis. The staining is cytoplasmic and is not extractable with 1% Triton X-100, which suggests that the psi-3 antigen is a structural component of the keratinocyte. Neither basal cells nor invading inflammatory cells are stained in psoriatic skin and the antigen appears to be associated specifically with maturing and not proliferating keratinocytes. Keratinocytes cultured in vitro from skin from nonpsoriatic individuals display the antigen in a granular pattern in differentiated cells. The antigen is also expressed after tape-stripping of normal skin and, therefore, represents an inducible product of normal keratinocytes. The antigen is destroyed by proteinase K and appears to be a protein. On discontinuous sodium dodecyl sulfate-gel electrophoresis, the antigen has been found to have a molecular weight of 135,000. The psi-3 antigen is interpreted as a new keratinocyte product expressed in psoriasis, culture, wound healing, and certain other pathologic skin conditions. The synthesis of such a new antigen would not be expected if keratinocyte maturation in psoriasis is a truncated version of the normal system and supports the hypothesis that psoriatic keratinocytes are following an alternative pathway. Results using experimental injury suggest that the psoriatic pathway is normally expressed during wound healing.