Interleukin-6 enhances human Ig production, but not as a terminal differentiation factor for B lymphocytes

The action of interleukin 6 on lymphoid populations

We have analysed the role of IL-6 in activation of human lymphocytes isolated from peripheral blood. We found little effect of IL-6 on proliferation of T cells. IL-6 did stimulate production of IgM by B cells. However, it did not behave as a terminal differentiation factor and was required only during the first two days of the culture. Under most conventional stimulation conditions T cells themselves produce little or no IL-6. High IL-6 production could be induced by stimulating the cells with a combination of phorbol-12-myristate 13-acetate (PMA) and anti-CD28 antibodies.

Effects of recombinant tumour necrosis factor (rTNF-alpha) in cancer. Observations on the acute phase protein reaction and immunoglobulin synthesis after high dose recombinant TNF-alpha administration in isolated limb perfusions in cancer patients

To obtain insight in the effect of TNF on the synthesis of acute phase proteins like CRP, alpha 1-antitrypsine, alpha 1-acidglycoprotein, C3 and C4 and the immunoglobulins (IgG-M-A), nine cancer patients who were treated with an isolated limb perfusion (ILP) with high dose recombinant TNF-alpha (rTNF-alpha) were investigated during a 7-day period after the end of the perfusion. Resorption of rTNF-alpha from out of these limbs into the circulation after the ILP induced within 30 min to 6 h in all patients elevated serum levels of IL-6. At the same time C-reactive protein became detectable in serum. The highest serum levels were obtained at 48 h after ILP. The serum levels of the other acute phase proteins (alpha 1-acidglycoprotein, alpha 1-antirypsine, C3, C4), rose more slowly and the highest serum levels were found at the third day. All investigated proteins declined after they had reached their peak levels. Levels of alpha 1-acidglycoprotein and alpha 1-anti-trypsin alpha 1-acid declined slower than both complement component. In regard to the immunoglobulin levels a nearly continuous increase in the serum level of specifically IgM was observed. This study clearly shows the interrelationship between TNF-alpha and IL-6 in regard to the synthesis of the different acute phase proteins; and moreover also a striking effect on IgM synthesis.

Squirrel monkey (Saimiri sciureus) B lymphocytes: secretion of IgG directed to Plasmodium falciparum antigens, by primed blood B lymphocytes restimulated in vitro with parasitized red blood cells

Blood B lymphocytes obtained from Plasmodium falciparum-immune Saimiri monkeys were assayed for their in vitro differentiation in immunoglobulin-secreting cells upon restimulation with P. falciparum-parasitized Saimiri red blood cells. Selected culture conditions enabled appropriately stimulated blood B cells to secrete 3F11/G10+ IgG, detected in the supernatants by means of a dot immunobinding assay. Primed blood B lymphocytes from P. falciparum-immune Saimiri monkeys were thus able to secrete IgG when restimulated by parasitized red blood cells in the presence of T cell- and monocyte-derived cytokines (recombinant human cytokines). These primed blood B cells, which were able to differentiate, were shown to secrete antibodies reactive with P. falciparum-infected red blood cells, as detected by means of an indirect immunofluorescence assay, and reactive with P. falciparum-infected red blood cell extracts, as detected by means of Western blot analysis. Furthermore, due to the possibility of discriminating between IgG subtypes in the squirrel monkey (3F11/G10+::3A2/G6+ IgG [associated with protection against the blood stages of P. falciparum] vs. 3F11/G10+::3E4/H8+ IgG [usually not functionally associated with protection]), we have attempted to estimate the respective proportions of each IgG subtype. In defined culture conditions, Saimiri monkey blood B cells preferentially secrete 3F11/G10+::3E4/H8+ IgG in response to parasitized red blood cells. We therefore discuss the conditions that would render this assay suitable for the selection, among P. falciparum blood stage antigens, of those that have major B-cell epitopes.

Interleukin-6, a new target for therapy in multiple myeloma?

During the past few years much insight has been gained into the immunobiology of multiple myeloma. It has become evident that the growth of myeloma cells is regulated by cytokines, notably interleukin-6. In this paper a brief review is given of the evidence derived from in vitro as well as in vivo observations that interleukin-6 is involved in the pathogenesis of multiple myeloma, and the implications of these findings for the development of new therapeutic strategies are discussed.

Interleukin 6 is not required for antigen-specific antibody responses by human B cells

Interleukin-6 (IL-6) is a late-acting differentiation factor for human B cells activated by polyclonal mitogens such as pokeweed mitogen (PWM) and Staphylococcus aureus Cowan strain I, but its role in specific antibody responses has not been established. We show here that IL-6 has no consistent effect on specific antibody responses by tonsillar mononuclear cells (TMC) stimulated with influenza virus. A blocking IL-6 antibody also had no effect on antibody production, suggesting that endogenous IL-6 production was not required. In control experiments, this antibody inhibited PWM-stimulated immunoglobulin secretion and proliferation of the IL-6-dependent B cell line B9. A requirement for IL-6 in responses of unfractionated TMC may have been disguised by the presence of T cells. To overcome this problem, we investigated the effect of IL-6 on specific antibody production by T-depleted B cells stimulated with antigen in the presence of IL-2, which is a T cell replacing factor (TRF) for human B cells. Specific antibody production was restored by IL-2, but not IL-6. Neither IL-6 nor anti-IL-6 antibody had any consistent effect on specific antibody production by purified B cells stimulated with antigen and TRF. These experiments show that IL-6 does not have a significant role in antigen (influenza virus)-specific antibody responses by human B lymphocytes.

On the interaction of IgG subclasses with the low affinity Fc gamma RIIa (CD32) on human monocytes, neutrophils, and platelets. Analysis of a functional polymorphism to human IgG2

An allotypic form of the low affinity IgG Fc receptor Fc gamma RIIa (CD32), termed low responder (LR) because of its weak reactivity with mouse (m) IgG1, interacts efficiently with human (h) IgG2. Fc gamma RIIaLR is the first known human FcR that binds this IgG subclass. In this study, we analyzed the role of Fc gamma RIIa in binding of stable hIgG-subclass dimers, and in induction of T cell mitogenesis using chimeric anti-CD3 mAb. We demonstrate that the functional polymorphism to hIgG2 is expressed on the majority of Fc gamma R-bearing peripheral blood cells: monocytes, neutrophils, and platelets. We were able to assess Fc gamma RII-mediated IgG-binding without interference of other Fc gamma R-classes, by blockade of Fc gamma RI on monocytes, and by using neutrophils of an individual deficient for the Fc gamma RIIIB gene. This study indicates as subclass specificity: hIgG3 >hIgG1,hIgG2 >> hIgG4 for Fc gamma RIIaLR and hIgG3,hIgG1 >> hIgG2 > hIgG4 for Fc gamma RIIaHR. Comparing the serum hIgG levels of individuals homozygous for the two fc gamma RIIa allotypic forms, we observed significantly lower hIgG2 serum levels in individuals expressing the hIgG2-binding LR allotypic form. This observation may implicate that Fc gamma RIIa regulates hIgG subclass production or turnover in man.