PLAZ~ZS 92 2"o 96 (Received for publication, July 24, 1959) The rheumatoid factor, a group of unusual macroglobulins, is demonstrable in the serum of the majority of patients with rheumatoid arthritis and in a relatively small proportion of patients with other diseases (1). The presence of this factor can be demonstrated by its reaction with human v-globulin (Cohn fraction II) in such serological procedures as the tanned sheep cell agglutination (2) and latex fixation tests (3), as well as by precipitin tests (4). The reactive component of "y-globulin seems to be an aggregate (5) with high sedimentation coefficients, which forms an insoluble complex with the rheumatoid factor. The origin and site of production of the rheumatoid factor has been unknown. I n the present study, fluorescein-labelled aggregated human 7-globulin was used as a specific reagent for its detection in situ. The results show that the factor is present in certain cells of the synovial tissues, lymph nodes, and subcutaneous nodules in active rheumatoid arthritis. Materials and MethodsFluorescein-Labdled Aggregated Human T-Globutin.--Human T-globulin (Cohn fraction II, E. R. Squibb Lot 1788), obtained as a gift from the American National Red Cross, was conjugated at a concentration of 20 rag. protein per ml. with fluorescein isothiocyanate (Sylvana Chemical Co., Orange, New Jersey), in accordance with the procedure of Riggs and associates (6), and dialyzed against buffered saline (0.15 ~ sodium chloride containing 0.01 M phosphate, pH 7.0) until free of unconjugated fluorescein. The fluorescein-labelled human "y-globuiin preparation was heated in a water bath to 62°C. for l0 minutes, and 40 per cent by volume of 2.18 M Na2SO, was then added, with stirring, in a manner used by Christian (5). A precipitate was collected after overnight storage in the cold, dissolved in saline, and dialyzed against phosphate buffer (0.15 x¢, pH 7.0). The dialyzed preparation was centrifuged at 18,400 a~.v.~, for 1 hour prior to use. This preparation will be referred to in this report as fluorescein-labelled aggregated human ~,-globulin. This reagent was six times more reactive in precipitation reactions with rheumatoid serums than a similarly prepared but unheated q,-globulin preparation, and furthermore was live times more reactive than a heated preparation in which the Na2SO4 treatment was omitted. The various preparations were also analyzed by ultracentrifugation. Finorescein-labelled aggregated human T-globulin contained approximately 34 per cent of the 7S component and 66 per cent of an aggregate having sedimentation coefficients varying from approximately 10S to 70S. The analysis was performed in a Spinco,

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A study was made of the cellular origin of human immunoglobulins (γ2, γ1M, γ1A). The results indicated that two closely related families of cells form immunoglobulins in human lymphoid tissue: germinal (reticular) centers and plasma cells. Thus their cellular origin in addition to their known antigenic relations further justifies placing the immunoglobulins in one family of proteins. Immunoglobulins were also formed to a small extent in primitive reticular cells which resembled those of germinal centers but were separated from them. Possibly such cells were undergoing transition to the much more numerous plasma cells with which they were commonly associated. The mantles of small lymphocytes which surrounded germinal centers did not contain detectable quantities of immunoglobulins. While in general only one type of immunoglobulin was present in an individual cell or germinal center, γ2- and γ1M-globulin were identified on occasion in the same plasma cell and germinal center. A peculiarity of the fetal thymus gland was the presence of immunoglobulin, mainly γ1M, in a small number of cells of small and intermediate size and primitive reticular appearance and in Hassall's corpuscles.