The rosette technique is used to visualize cell surface receptors. Human lymphocytes can form rosettes with sheep red blood cells (SRBC), indicating the presence of surface receptors. This technique has been used to study the surface markers of human T and B lymphocytes. It was found that a large population of human lymphocytes form rosettes with SRBC, which is not explained by binding to immunocompetent cells reactive against SRBC. These rosettes are called immune rosettes. The rosette-forming lymphocytes consist of antibody-producing cells and bone marrow-derived B lymphocytes. Whether thymus-derived T lymphocytes can form rosettes remains uncertain. Spontaneous rosette-forming lymphocytes have immunoglobulin receptors and their rosette-forming ability can be blocked by pretreating with anti-Ig sera or anti-lymphocyte sera (ALS). The blocking capacity of these rosettes is positively correlated with the immunosuppressive effect of ALS in humans. In 1970, it was observed that human lymphocytes formed spontaneous rosettes with SRBC in high percentages. The E-binding lymphocytes were investigated for Ig determinants and their ability to bind erythrocyte-antibody-complement (EAC). These complement-covered RBC bind to lymphocytes via the receptor for activated C3. Further characterization of E rosette formation was presented. The study showed that a high percentage of peripheral blood lymphocytes formed E rosettes, with almost 100% of thymocytes forming rosettes. The percentage of E-binding lymphocytes varied slightly depending on their location on the glass slide. The binding between lymphocytes and SRBC is weak, so care must be taken when resuspending the rosettes. No movement of the cells on the glass slide should be allowed. A small contamination of other leukocytes is demonstrated by May-Grünwald Giemsa-stained smears. Lymphocytes forming EAC rosettes were found in five cases, with HRBC tightly bound to the lymphocytes. These rosettes can be produced and kept at 37°C, unlike E rosettes. No mixed rosettes were observed where lymphocytes bound both SRBC and HRBC. This was possible to determine as the HRBC and SRBC differ in size. Occasionally, rosettes were in clumps and it was difficult to exclude mixing of the signal cells bound to the surface. This difficulty was overcome by labeling the SRBC with FITC which allowed inspection of the rosettes in UV light. Lymphocytes bearing Ig determinants were found in 20–44% of peripheral lymphocytes, but no thymocytes. Most of the lymphocyte surface was available for inspection as the SRBC were mostly bound in a ring around the surface and did not cover it completely. Some nonrosette-formingThe rosette technique is used to visualize cell surface receptors. Human lymphocytes can form rosettes with sheep red blood cells (SRBC), indicating the presence of surface receptors. This technique has been used to study the surface markers of human T and B lymphocytes. It was found that a large population of human lymphocytes form rosettes with SRBC, which is not explained by binding to immunocompetent cells reactive against SRBC. These rosettes are called immune rosettes. The rosette-forming lymphocytes consist of antibody-producing cells and bone marrow-derived B lymphocytes. Whether thymus-derived T lymphocytes can form rosettes remains uncertain. Spontaneous rosette-forming lymphocytes have immunoglobulin receptors and their rosette-forming ability can be blocked by pretreating with anti-Ig sera or anti-lymphocyte sera (ALS). The blocking capacity of these rosettes is positively correlated with the immunosuppressive effect of ALS in humans. In 1970, it was observed that human lymphocytes formed spontaneous rosettes with SRBC in high percentages. The E-binding lymphocytes were investigated for Ig determinants and their ability to bind erythrocyte-antibody-complement (EAC). These complement-covered RBC bind to lymphocytes via the receptor for activated C3. Further characterization of E rosette formation was presented. The study showed that a high percentage of peripheral blood lymphocytes formed E rosettes, with almost 100% of thymocytes forming rosettes. The percentage of E-binding lymphocytes varied slightly depending on their location on the glass slide. The binding between lymphocytes and SRBC is weak, so care must be taken when resuspending the rosettes. No movement of the cells on the glass slide should be allowed. A small contamination of other leukocytes is demonstrated by May-Grünwald Giemsa-stained smears. Lymphocytes forming EAC rosettes were found in five cases, with HRBC tightly bound to the lymphocytes. These rosettes can be produced and kept at 37°C, unlike E rosettes. No mixed rosettes were observed where lymphocytes bound both SRBC and HRBC. This was possible to determine as the HRBC and SRBC differ in size. Occasionally, rosettes were in clumps and it was difficult to exclude mixing of the signal cells bound to the surface. This difficulty was overcome by labeling the SRBC with FITC which allowed inspection of the rosettes in UV light. Lymphocytes bearing Ig determinants were found in 20–44% of peripheral lymphocytes, but no thymocytes. Most of the lymphocyte surface was available for inspection as the SRBC were mostly bound in a ring around the surface and did not cover it completely. Some nonrosette-forming