The study concerned the binding of sheep red blood cells by human peripheral blood lymphocytes. The results indicate that the phenomenon (rosette formation) is probably dependent on thymus‐derived lymphocytes (T lymphocytes) and not due to bone marrow lymphocytes (B lymphocytes). These data were obtained by a gradient centrifugation technique separating B lymphocytes from rosette‐forming cells, by direct study of B lymphocytes and rosette‐forming cells in the same preparations, and from the study of patients with selective immunodeficiency diseases and chronic lymphocytic leukaemia. Furthermore, inhibition of rosette formation was absent or very weak after incubation of lymphocytes with anti‐immunoglobulin antisera, but considerable following their incubation with unspecific mitogens (phytohaemagglutinin, pokeweed mitogen, concanavalin A, anti‐lymphocyte antiserum) and also after trypsin treatment. Incubation temperature was important for the frequency of rosettes, and experiments with metabolic inhibitors showed that to form rosettes the lymphocytes required an intact energy production.

Objective: To investigate the possible role of osteoprotegerin (OPG) in bone metabolism in humans by measuring serum levels of OPG in ®ve well-characterized patient populations with known or suspected pathology in bone homeostasis, but with differences in the pathogenesis of these disturbances. Design: The study comprised 34 patients with Cushing's syndrome (CS), 24 acromegalic patients, 16 patients with growth hormone de®ciency (GHD), 29 HIV-infected patients, 25 patients with common variable immunode®ciency (CVI) and 59 age-and sex-matched healthy controls (CTR). Methods: Serum levels of tumor necrosis factor (TNF)-a, OPG, C-terminal telopeptides of Type-I collagen (CTX-I) and osteocalcin were determined in all study subjects as well as cortisol (CS and CTR) and IGF-I (acromegaly, GHD and CTR). Results: OPG levels were signi®cantly elevated in both CVI (median increase ,32%, P , 0X05 and HIV-infected patients with especially high levels in the latter group (,52%, P , 0X001Y signi®cantly correlated with increased TNFa levels r 0X47Y P , 0X02X Also CS patients had elevated serum OPG (,24%, P , 0X01Y signi®cantly correlated with increased serum cortisol r 0X35Y P , 0X05X In contrast, OPG levels in acromegalic and GHD patients were not different from healthy controls. No relationships were found between OPG levels and CTX-I or osteocalcin. Conclusions: These ®ndings suggest that enhanced OPG levels may be a compensatory response to enhanced osteoclast activity or negative bone remodeling balance in some conditions, but may also be a parameter of enhanced activity in the OPG system possibly correlated to enhanced activity of other members of the TNF family.

Summary Common variable immunodeficiency (CVID) is