Interleukin-15 (IL-15) is a 14-to 15-kDa member of the 4 α-helix bundle family of cytokines. IL-15 expression is controlled at the levels of transcription, translation, and intracellular trafficking. In particular, IL-15 protein is posttranscriptionally regulated by multiple controlling elements that impede translation, including 12 upstream AUGs of the 5 UTR, 2 unusual signal peptides, and the C-terminus of the mature protein. IL-15 uses two distinct receptor and signaling pathways. In T and NK cells the IL-15 receptor includes IL-2/15Rβ and γ c subunits, which are shared with IL-2, and an IL-15-specific receptor subunit, IL-15Rα. Mast cells respond to IL-15 with a receptor system that does not share elements with the IL-2 receptor but uses a novel 60-to 65-kDa IL-15RX subunit. In mast cells IL-15 signaling involves Jak2/STAT5 activation rather than the Jak1/Jak3 and

The fluid mosaic membrane model proved to be a very useful hypothesis in explaining many, but certainly not all, phenomena taking place in biological membranes. New experimental data show that the compartmentalization of membrane components can be as important for effective signal transduction as is the fluidity of the membrane. In this work, we pay tribute to the Singer-Nicolson model, which is near its 30th anniversary, honoring its basic features, ''mosaicism'' and ''diffusion,'' which predict the interspersion of proteins and lipids and their ability to undergo dynamic rearrangement via Brownian motion. At the same time, modifications based on quantitative data are proposed, highlighting the often genetically predestined, yet flexible, multilevel structure implementing a vast complexity of cellular functions. This new ''dynamically structured mosaic model'' bears the following characteristics: emphasis is shifted from fluidity to mosaicism, which, in our interpretation, means nonrandom codistribution patterns of specific kinds of membrane proteins forming smallscale clusters at the molecular level and large-scale clusters (groups of clusters, islands) at the submicrometer level. The cohesive forces, which maintain these assemblies as principal elements of the membranes, originate from within a microdomain structure, where lipid-lipid, protein-protein, and protein-lipid interactions, as well as sub-and supramembrane (cytoskeletal, extracellular matrix, other cell) effectors, many of them genetically predestined, play equally important roles. The concept of fluidity in the original model now is interpreted as permissiveness of the architecture to continuous, dynamic restructuring of the molecular-and higherlevel clusters according to the needs of the cell and as evoked by the environment.

We studied purified subpopulations of lymphocytes from patients with the acquired immunodeficiency syndrome (AIDS) in order to determine whether intrinsic defects in lymphocyte function, aside from those due to alterations in lymphocyte numbers, were present. Mitogen-stimulated DNA synthesis, production of gamma interferon, production of interleukin-2, and expression of interleukin-2 receptors, although variably decreased in unseparated cell populations, were normal in populations of purified T-cell subsets. In contrast, DNA synthesis in response to the soluble protein antigen tetanus toxoid was decreased in both unseparated and purified T-cell subpopulations. Cell-mixing experiments demonstrated that the hyporesponsiveness of the unfractionated lymphocytes from patients with AIDS was not due to active suppression. We conclude that the lymphocytes of patients with AIDS, although capable of undergoing a normal degree of blast transformation and lymphokine production after mitogenic stimulation, have an intrinsic defect in their ability to recognize and respond to soluble antigen.

Human interleukin-2 (IL-2) is a glycoprotein of relative molecular mass (Mr) 15,000, which is released by T lymphocytes on stimulation with antigen or mitogen and functions as a T-cell growth factor (TCGF) by inducing proliferation of activated T cells. It is generally accepted that resting or activated B cells do not respond directly to IL-2 but require for their proliferation other T-cell-derived lymphokines usually referred to as B-cell growth factors (BCGFs). Recently, however, a monoclonal antibody reacting with the IL-2 receptor molecules expressed by activated T cells (anti-Tac) was shown to react also with certain B tumour cells; in addition, murine B cells proliferate in response to pure human IL-2. We now show that recombinant IL-2, derived from Escherichia coli expressing the human gene, is able to promote strong proliferation of human B cells activated with protein-A-rich Staphylococcus aureus Cowans strain I. Moreover, we demonstrate that the anti-Tac antibody also reacts with S. aureus-activated normal B cells and inhibits sharply the proliferative response of such cells to IL-2. Finally, immunoprecipitation experiments reveal that anti-Tac defines similar molecules on activated T and B cells.

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We have investigated suppressor T-cell activity in female NZB/NZW F1 mice using PWM-driven IgM biosynthesis in vitro as an indicator system. In initial we studied we observed that spleen cells from normal mice (BALB/c, C57BL/6), as well as from young (4 wk) and adult (18 wk) NZB/NZW mice, cultured in the presence of PWM synthesize 860 +/- 120 ng IgM/10(6) cells/7 days. However, when Con A (at 2 mug/ml) was added directly to the cultures (along with PWM), cells obtained from adult normal mice and young NZB/NZW mice showed a 94% suppression of IgM synthesis, whereas cells obtained from adult NZB/NZW mice were suppressed significantly less. To analyze these findings we studied the effect of Con A-induced suppressor cells (cells cultured with Con A for 24 h and washed free of Con A) on PWM-driven IgM biosynthesis. Spleen cells obtained from normal mice cultured in the presence of Con A-pulsed cells obtained from normal mice and young NZB/NZW mice showed an 83-88% suppression of PWM-driven IgM synthesis. Similarly, supernates obtained from Con A-pulsed cells of normal mice or of young NZB/NZW mice suppressed PWM-driven IgM synthesis. This suppression by Con A-pulsed cells and their supernates required T cells since T-cell fractions but not B-cell fractions eluted from anti-Fab Sephadex columns mediated suppression of co-cultured normal cells; in addition, Con A-pulsed cells treated with anti-theta and complement do not mediate suppression. These studies of Con A-induced suppressor cell activity in normal mice and young NZB/NZW mice contrast with studies of Con A-induced suppressor cell activity in adult NZB/NZW mice. We found that adult NZB/NZW Con A-pulsed cells and supernates obtained from the Con A-pulse cells had vastly decreased suppressor potential; in this case the Con A-pulse cells and supernatant fluids derived from such cells did not suppress PWM-driven IgM synthesis by normal cells. Finally, whereas spleen cells from young and adult NZB/NZW mice differ in their suppressor cell potential, cells from both sources could respond equally to suppressor signals in that Con A-pulsed normal cells or supernates derived from such cells caused equivalent suppression of PWM-driven IgM synthesis by young and adult NZB/NZW cells. These observations allow us to conclude that NZB/NZW mice lose suppressor T-cell activity as they age.

We undertook clinical, immunologic, and endocrinologic studies of a family in which two brothers and their two maternal uncles had a similar disorder characterized by hypogammaglobulinemia and isolated growth hormone deficiency. Recurrent sinopulmonary infections were a prominent feature in two patients. All patients had short stature and retarded bone age during childhood, and the adults had delayed onset of puberty. The immunodeficiency was characterized by absent specific antibody production in vivo and impaired immunoglobulin production in vitro. Three of the four patients lacked circulating B lymphocytes, even though tonsils were present in those patients. All patients had deficient growth hormone responses to insulin and arginine or levodopa. These patients have an X-linked recessive disorder, but their immunodeficiency differs from the X-linked immune disorders in the World Health Organization classification; their X-linked pattern of growth hormone deficiency, without other endocrine abnormality, is also unique.