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Notes: Recently, monoclonal antibodies capable of phenotyping malignant lymphomas in routinely fixed and processed tissue have become available. Some of these reagents identify lineage-restricted variants of the leucocyte common molecule, whereas others identify unique fixation-resistant epitopes on lymphoid cells, some of which are shared by non-lymphoid tissues. A new generation of antibodies recognizing ‘classical’ leucocyte antigens such as CD3 are also emerging. Refinements in antigen detection systems, especially for immunoglobulin recognition, combined with these new reagents promise to improve the accuracy of lymphoma diagnosis in routine histopathology. These new antibodies are reviewed, and their limitations, cross reactivities and profiles of staining in lymphoreticular disease are discussed. A strategy for their optimal use is proposed.

Notes: Recently, monoclonal antibodies capable of phenotyping malignant lymphomas in routinely fixed and processed tissue have become available. Some of these reagents identify lineage-restricted variants of the leucocyte common molecule, whereas others identify unique fixation-resistant epitopes on lymphoid cells, some of which are shared by non-lymphoid tissues. A new generation of antibodies recognizing ‘classical’ leucocyte antigens such as CD3 are also emerging. Refinements in antigen detection systems, especially for immunoglobulin recognition, combined with these new reagents promise to improve the accuracy of lymphoma diagnosis in routine histopathology. These new antibodies are reviewed, and their limitations, cross reactivities and profiles of staining in lymphoreticular disease are discussed. A strategy for their optimal use is proposed.

Notes: Fourteen plasma cell tumours, including examples of solitary plasmacytoma and multiple myeloma, were studied with a panel of antibodies reactive in formalin-fixed, paraffin wax-embedded tissue. Each case showed immunoglobulin light chain restriction. Five tumours were reactive with antibodies to cytokeratin. Of these five cases, four were negative with antibodies to leucocyte common antigen and only one was weakly positive. Anti-cytokeratin reactivity by plasma cell tumours is more common than was originally anticipated and represents an important diagnostic pitfall.

Notes: We describe the clinical presentation, morphology, immunophenotypic features and molecular biology of seven cases of conjunctival lymphoid infiltration. In five cases there was either immunophenotypic or molecular evidence of B-cell lymphoma. Each of these cases showed the morphological, immunophenotypic and molecular feature of low-grade B-cell lymphoma of mucosa-associated lymphoid tissue (MALT) type. The findings suggest that most conjunctival lymphomas are of this type and explains their uniformly favourable prognosis.

Notes: Aims: Splenic marginal zone lymphoma (SMZL) is characterized by a micronodular infiltrate of the splenic white pulp, centred on pre-existing follicles, with a peripheral rim of ‘marginal’ zone B-cells, always accompanied by a variable degree of red pulp infiltration. These histological features can be closely mimicked by a variety of other small B-cell lymphomas when they involve the spleen, which makes recognition of SMZL difficult. We therefore have compared the histopathological and immunohistochemical features of other non-Hodgkin's lymphoma (NHL) types with those of SMZL.〈section xml:id="abs1-1"〉〈title type="main"〉Methods and resultsWe selected cases of splenic involvement by different types of B-cell lymphoma, including mantle cell lymphoma (MCL), follicular lymphoma (FL), immunocytoma (IM) and lymphocytic lymphoma (B-CLL). A micronodular pattern and marginal zone differentiation were both found to be frequently present in FL and MCL, and with lesser frequency in IM and B-CLL. The main morphological feature useful for differential diagnosis was the cytological composition of the white pulp tumoral nodules. SMZL is distinguished by characteristic dimorphic cytology, different from the monomorphic cytology of MCL, and the distinctive mixture of centroblasts and centrocytes which is the rule in FL. B-CLL could also be identified on the basis of the polymorphic cytology including small lymphocytes and prolymphocytes, whereas cases diagnosed as IM show prominent plasmacytic differentiation, lacking the features of the other lymphoma types. Immunohistochemistry was particularly useful for the differential diagnosis. Thus the recognition of MCL was facilitated by the identification of cyclin D1 and CD43 reactivity, while FL could be recognized by the lack of IgD expression or the distinctive pattern of Ki67 staining found in SMZL. B-CLL cells were CD23 + , CD43 +.〈section xml:id="abs1-2"〉〈title type="main"〉ConclusionThe results of this study provide morphological and immunohistological information useful in the recognition of the different varieties of NHLs when involving the spleen and the differential diagnosis of SMZL.

Notes: To describe and illustrate a novel and highly sensitive peroxidase-based immunohistochemical detection system which employs mutually attractive, mirror image complementary antibodies (MICA).〈section xml:id="abs1-2"〉〈title type="main"〉Methods and resultsTo demonstrate the sensitivity of the MICA system alongside the avidin–biotin complex (ABC) method, we selected a range of mouse monoclonal and rabbit polyclonal primary antibodies against antigens that are generally regarded as relatively difficult or impossible to detect on formalin-fixed, paraffin-embedded lymphoid tissue. Compared with the ABC method, the MICA immunodetection method enabled us to dilute primary antibodies up to 200-fold with equivalent or superior immunostaining results and, usually, considerably shortened primary antibody incubation times.〈section xml:id="abs1-3"〉〈title type="main"〉ConclusionsWe have described and illustrated a novel immunohistochemical detection system and demonstrated greatly increased sensitivity over the commonly used ABC system. An additional advantage of the MICA system is that it is avidin-free and so avoids non-specific staining due to endogenous tissue biotin.