Type I cytokine profiles of human naïve and memory B lymphocytes: a potential for memory cells to impact polarization.

B cells bifurcating along 'type 1' or 'type 2' pathways under the influence of polarizing cytokines can, in turn, influence the direction of an immune response. Here, we compare the capacity of human B cells residing within naïve and memory compartments to participate in type 1 polarizing responses. B-cell receptor (BCR) engagement provided the main signal for interleukin (IL)-12Rbeta1 expression in the two subsets: this was potentiated by CD154 together with interferon-gamma (IFN-gamma) but inhibited by IL-12. IL-12Rbeta2 could be induced on a minority of B cells by the same signals, and also by IFN-gamma alone. WSX-1, a receptor for IL-27, was expressed in both subsets with no evidence for its regulation by the signals studied. While neither subset was capable of secreting much IL-12 p70, memory B cells could produce a small amount of IL-12 p40 on CD40 ligation. Memory B cells also, exclusively, expressed IL-23 p19 mRNA on BCR triggering. Importantly, products of appropriately stimulated memory--but not naive--B cells were shown to promote the synthesis of IFN-gamma in uncommitted T-helper cells. The data indicate an equal capacity for naïve and memory B cells to respond within a type 1 polarizing environment. Although poorly equipped for initiating type 1 responses, B cells--by virtue of the memory subset--reveal a capacity for their maintenance and amplification following T-dependent signalling.

HL60 cells halted in G1 or S phase differentiate normally.

Differentiating agents regulate the proliferation and myeloid maturation of HL60 cells by mechanisms that are at least partly independent (Drayson et al., (2001), Exp. Cell Res. 266, 126-134). We have investigated whether halting HL60 cells in G1 or S phase influences their commitment to or maturation along the neutrophil and monocyte pathways. Early G1 and S phase cells were isolated separately by elutriation. Quinidine was used to block the cell cycle progression of G1 cells and aphidicolin to greatly retard the progression of S phase cells. Neutrophilic (in response to all-trans-retinoic acid) or monocytic (to 1 alpha,25-dihydroxyvitamin D(3)) differentiation were assessed by induction of CD11b, M-CSF receptor and CD14 expression, acquisition of granulocyte-colony stimulating factor responsiveness, capacities to phagocytose yeast and reduce nitroblue tetrazolium, and down-regulation of CD30 and transferrin receptor expression. The cell-cycle-blocked cells differentiated at normal rates, mostly without incorporating bromodeoxyuridine. These observations establish: (a) that neither transit through the cell cycle nor a cell's position in the cell cycle substantially influences execution of the neutrophilic and monocytic differentiation programs by HL60 cells; and (b) that individual HL60 cells are genuinely bipotent.

Low-level hypermutation in T cell-independent germinal centers compared with high mutation rates associated with T cell-dependent germinal centers.

Exceptionally germinal center formation can be induced without T cell help by polysaccharide-based antigens, but these germinal centers involute by massive B cell apoptosis at the time centrocyte selection starts. This study investigates whether B cells in germinal centers induced by the T cell-independent antigen (4-hydroxy-3-nitrophenyl)acetyl (NP) conjugated to Ficoll undergo hypermutation in their immunoglobulin V region genes. Positive controls are provided by comparing germinal centers at the same stage of development in carrier-primed mice immunized with a T cell-dependent antigen: NP protein conjugate. False positive results from background germinal centers and false negatives from non-B cells in germinal centers were avoided by transferring B cells with a transgenic B cell receptor into congenic controls not carrying the transgene. By 4 d after immunization, hypermutation was well advanced in the T cell-dependent germinal centers. By contrast, the mutation rate for T cell-independent germinal centers was low, but significantly higher than in NP-specific B cells from nonimmunized transgenic mice. Interestingly, a similar rate of mutation was seen in extrafollicular plasma cells at this stage. It is concluded that efficient activation of hypermutation depends on interaction with T cells, but some hypermutation may be induced without such signals, even outside germinal centers.