Differentiation, identification and enumeration of sub-populations of lymphocytes including B-cells and T-cells can now be further discriminated into their sub-populations by means of basic orange 21 as a supravital stain to provide distinctive morphologic differences between B-cells, T-suppressor cells, T-helper cells and natural killer (NK) cells without resorting to the use of individual monoclonal antibodies for differentiation of each of the above. The differentiation, identification and enumeration of the foregoing cells can be accomplished by means of both white light absorbance and fluorescence measurements, singly or in sequential combinations.

An article for performing solid-phase immunological assays and methods for performing assays utilizing such article. A solid-phase support suitable for immunological assays is stained with an organic dye that has a net-positive charge and a hydrophobic aromatic ring structure. An immunologically reactive component having a net-negative charge, such as a whole cell, is securely immobolized by the dye to the support through noncovalent interactions. A sample of biological fluid may be added to the article to which the immunologically reactive component has been immobilized to effect binding of antigens or antibodies in the sample which are specific to the immobilized component. The presence of the antigen-antibody complex may then be determined by any known means.