IL-4 promotes the migration of circulating B cells to the spleen and increases splenic B cell survival.

We report that IL-4 causes a redistribution of B cells and modestly increases B cell life span. Intravenous injection of a long-acting formulation of IL-4 induces increases in both spleen cell number and the percentage of splenic B cells. These effects are observed within 1 day of IL-4 administration and plateau after approximately 3 days if IL-4 treatment is continued. The increase in splenic B cell number is IL-4 dose dependent, CD4+ T cell independent, FcgammaRII/FcgammaRIII independent, and Stat6 independent. Decreases in the number of B cells in the blood and the percentage of mature B cells in the bone marrow, concomitant with the increase in splenic B cell number, suggest that redistribution of circulating B cells to the spleen is partially responsible for IL-4 induction of splenic B cell hyperplasia. Considerable reduction in the effect of 5 days of IL-4 treatment on splenic B cell number when B lymphopoiesis is blocked with anti-IL-7 mAb suggests that generation of new B cells is also involved in IL-4-induced splenic B cell hyperplasia. 5-Bromo-2'-deoxyuridine labeling experiments demonstrate that IL-4 modestly prolongs the life span of newly generated splenic B cells, and experiments that measure B cell HSA (CD24) expression as an indicator of B cell age suggest that IL-4 may also prolong the life span of mature splenic B cells. Thus, IL-4 increases splenic B cell number through two Stat6-independent effects: increased net migration of circulating B cells to the spleen and increased B cell life span. Both effects may promote Ab responses to a systemic Ag challenge.

In vivo survival of autoreactive B cells: characterization of long-lived B cells.

To determine the effects of chronic Ag stimulation on B cell survival and phenotype, we compared survival and surface markers of hen egg lysozyme (HEL)-specific B cells in Ig transgenic (Tgn) mice, which lack HEL, and in HEL-Ig transgenic mice, which express soluble HEL. Serum HEL levels were maximized in HEL-Ig Tgn mice by feeding them zinc, which activates the metallothionein promoter that regulates HEL expression. B cell age was characterized by expression of heat-stable Ag, and B220 and B cell survival was studied by evaluating changes in B cell number when lymphopoiesis was suppressed with anti-IL-7 mAb and by identifying newly generated B cells through 5-bromo-2'-deoxyuridine incorporation. Our observations show that the mean B cell life span is considerably reduced in HEL-Ig Tgn compared with Ig Tgn mice, but also demonstrate that some HEL-Ig Tgn B cells survive to maturity. Some of these surviving B cells have undergone receptor editing (substitution of an endogenous Ig light chain for the transgenic Ig light chain), so that their ability to bind HEL is decreased or absent. Surviving HEL-Ig Tgn B cells that retain HEL specificity express decreased mIgD and little or no mIgM. mIgD expression progressively decreases with increasing HEL-Ig Tgn B cell age. These observations suggest that self Ag-specific B cells can survive in the presence of soluble self Ag by down-regulating mIg expression, which should limit B cell signaling by Ag that might otherwise cause deletion of these cells.

Stat6 regulation of in vivo IL-4 responses.

Although in vitro development of a Th2 response from naive CD4+ T cells is Stat6 dependent, mice immunized with a goat Ab to mouse IgD have been reported to produce a normal primary IL-4 response in Stat6-deficient mice. Experiments have now been performed with mice immunized with more conventional Ags or inoculated with nematode parasites to account for this apparent discrepancy. The ability of an immunogen to induce a primary in vivo IL-4 response in Stat6-deficient mice was found to vary directly with its ability to induce a strong type 2 cytokine-biased response in normal mice. Even immunogens, however, that induce strong primary IL-4 responses in Stat6-deficient mice induce poor memory IL-4 responses in these mice. Consistent with this, Stat6-deficient CD4+ T cells make relatively normal IL-4 responses when stimulated in vitro for 3 days with anti-CD3 and anti-CD28, but poor IL-4 responses if they are later restimulated with anti-CD3. Thus, Stat6 signaling enhances primary IL-4 responses that are made as part of a type 0 cytokine response (mixed type 1 and type 2) and is required for normal development or survival of Th2 memory cells.

Stat6 signaling promotes protective immunity against Trichinella spiralis through a mast cell- and T cell-dependent mechanism.

Studies in mice infected with the gastrointestinal nematode parasite Nippostrongylus brasiliensis demonstrated that IL-4/IL-13 activation of Stat6 suppresses development of intestinal mastocytosis and does not contribute to IL-4/IL-13 production, but is still essential for parasite expulsion. Because expulsion of another gastrointestinal nematode, Trichinella spiralis, unlike N. brasiliensis expulsion, is mast cell dependent, these observations suggested that T. spiralis expulsion would be Stat6 independent. Instead, we find that Stat6 activation by IL-4/IL-13 is required in T. spiralis-infected mice for the mast cell responses that induce worm expulsion and for the cytokine responses that induce intestinal mastocytosis. Furthermore, although IL-4 induces N. brasiliensis expulsion in the absence of B cells, T cells, and mast cells, mast cells and T cells are required for IL-4 induction of T. spiralis expulsion. Thus, Stat6 signaling is required for host protection against N. brasiliensis and T. spiralis but contributes to expulsion of these two worms by different mechanisms. The induction of multiple effector mechanisms by Stat6 signaling provides a way for a cytokine response induced by most gastrointestinal nematode parasites to protect against most of these parasites, even though different effector mechanisms are required for protection against different nematodes.

[Prevention of binding of Nile red with hydrophobic proteins and surface cuvettes using detergents]. / Predotvrashchenie sviazyvaniia nil'skogo krasnogo s gidrofobnymi belkami i poverkhnost'iu kiuvety s pomoshch'iu detergenta.

The nile red fluorescence in solutions containing Triton X-100, human serum albumin and hexadecane in different combinations was investigated. The dye fluorescence in phosphate buffer after 2-4 min incubation strongly decreased because of the dye aggregation and was stable in a detergent solution. The intensity of nile red fluorescence in the detergent solution was not changed after the addition of equal weight concentration of albumin and increased more than 2 times after the addition of the same concentration of hexadecane. The detergent eliminated the nile red sorption by cuvette surface. It is concluded that the detergent addition increases nile red selectivity as a lipid probe in the lipid-protein systems.

[The biological effect of low-level radiation doses on the morphological composition of the peripheral blood in children]. / Biologicheskii éffekt malykh doz radiatsii na morfologicheskii sostav perifericheskoi krovi u detei.

Examination of 339 children at the age of 2 to 12 years, living in the caesium contaminated region (from 2 to 5 Ci/km2) has revealed that total radioactivity of their urine is, on the average, twice as high as that of children living in "pure" regions. Quantitative and qualitative changes were observed in the erythroid series, neutrophilic leukocytes, eosinophils and B-lymphocytes of the peripheral blood of children subjected to long-term low-level irradiation. It should be noted that the character and direction of these changes were a function of the children's age and the level of total radioactivity of their urine.