In vitro synthesis of human IgE by neonatal lymphocytes: enhancing effect of interferon-gamma

Can cord blood cells support the cytokine storm in GvHD?

Cord blood has a high number of proliferating hematopoietic progenitors and is therefore used as an alternative source of hematopoietic cells for allogeneic transplantation. In addition there is a wider availability of cord blood and a lower cost of procurement compared to bone marrow. However one of the most interesting immunological benefits of a cord blood transplant that has been proposed is the low severity of Graft versus Host Disease (GvHD). This review aims to address some of the immunological reasons why this may be the case by assessing the role of cord blood cytokines in the cytokine storm of GvHD.

In vitro release of soluble CD23 by human lymphocytes in ragweed-sensitive versus nonatopic patients following stimulation with ragweed antigen E

BACKGROUND

Soluble CD23 is the proteolytic cleavage product of the low affinity receptor (FcERII). Functions of CD23 and its soluble products may include upregulation of IgE production and stimulation of B lymphocyte growth.

METHODS

Soluble CD23 was quantitated in supernatants of lymphocytes from nine ragweed-sensitive and eight nonatopic subjects stimulated in vitro by antigen E (amb Al), crude ragweed extract, and pokeweed mitogen (PWM).

RESULTS

Although PWM stimulation produced no significant difference between groups, sCD23 release was significantly elevated in the cells of nonatopic patients stimulated with antigen E and crude ragweed extract (P less than .05).

CONCLUSIONS

This finding supports the concept of separate pathways of activation by antigen and mitogen for sCD23 release and suggests ragweed-sensitive and nonatopic patients have fundamental differences in the response of sCD23 release to ragweed antigen stimulation.

Development of mucosal immune function in man: potential for GI disease states

The human mucosal immune system is structurally mature and has all the necessary cellular components to generate an immune response at birth. However, in the absence of dietary antigens and bacterial flora, there are no secondary follicles in the Peyer's patches and virtually no immunoglobulin A plasma cells in the lamina propria. Reactive follicle centers develop after birth but it takes 2 years for mucosal IgA plasma cell density to reach adult levels. T cells are present in the epithelium and lamina propria at birth, albeit at a lower frequency than later in life and there are major differences in phenotype between T cells in fetal intestine and postnatal intestine. There is no information on the impact of the massive antigenic challenge at birth on the mucosal immune system. Well-documented deficiencies in the ability of the blood T cells of the neonate to produce interleukin-4 and interferon-gamma may also occur in the intestine. It is still an open question whether it is better to try to prevent immunological sensitization of the newborn by avoiding potential allergens (i.e. cow's milk), or whether early exposure (as happens when premature infants are given formula feeds) might tolerize the infant. Hydrolysed cow's milk formulae are probably less antigenic than whole cow's milk and have been widely used in the treatment of cow's milk allergy. Some thought is now being given as to whether the prophylactic use of hydrolysates can reduce cow's milk allergy in 'at-risk' infants.

Depletion of IgM xenoreactive natural antibodies by injection of anti-mu monoclonal antibodies

It is believed that IgM xenoreactive natural antibodies (XNA) and activation of complement are the two main effectors involved in the hyperacute rejection (HAR) of discordant xenografts, such as pig-to-primate kidney, liver or heart transplants. We have hypothesized that long-term depletion of circulating IgM XNA might be able to overcome HAR and induce the "accommodation" of pig-to-primate vascular discordant xenografts. Several techniques have been described to eliminate circulating XNA in primates but, up to now, none has been able to totally deplete these antibodies for a sufficiently long period of time in order to test the hypothesis of discordant xenograft "accommodation". Previous reports from our laboratory have shown that, in rodents, B-cell immunosuppression could be achieved by neonatal administration of anti-mu antibodies. Recently we have shown that administration of an anti-mu mAb, in adult rats, was able to totally deplete circulating IgM and IgM XNA, without immune complex disease. Furthermore, we have used different methods such as splenectomy, plasma exchange and an anti-B cell immunosuppressive agent mycophenylate mophetil (RS61443, Syntex, Palo Alto, USA) to pre-deplete circulating IgM before administration of anti-mu mAb (MARM-7) and showed that the effectiveness of anti-mu mAb to deplete circulating IgM was increased by 100-fold. Depletion of circulating IgM in adult rats by anti-mu mAb (MARM-7) was used as an experimental model to study the role of IgM XNA in the pathogenesis of HAR in guinea pig-to-rat cardiac xenografts. Our data show that IgM XNA play a major role in HAR, even if in this discordant combination direct activation of complement, probably through the alternative pathway, seems to be the main effector involved in HAR. We have analyzed the mechanisms of anti-mu depletion of circulating IgM in adult animals and shown that, besides anti-mu/IgM immune complex formation, depletion of circulating IgM results from the very significant inhibition of B-cell differentiation and secretion of IgM following in vivo crosslinking and internalization of surface IgM on B cells. As well, we provide evidence demonstrating that anti-mu mAb blocks B cells at an early stage of maturation, probably in the bone marrow. Furthermore, we have developed several rat anti-human and anti-baboon IgM mAb and tested their ability to deplete circulating IgM and IgM XNA in baboons, after splenectomy or splenectomy and plasma exchange.(ABSTRACT TRUNCATED AT 400 WORDS)

Interferon-gamma production by cord-blood mononuclear cells is reduced in newborns with a family history of atopic disease and is independent from cord blood IgE-levels

For newborn children both elevated serum IgE levels in the cord blood and a positive family history of atopic disease have been shown to be risk factors for the manifestation of atopic diseases. In adult patients with atopic dermatitis, in vitro interferon-gamma (IFN-gamma) production is reduced and a negative correlation with serum IgE levels has been shown. We have now raised the question if newborn infants at risk for the development of atopic disease have similar abnormalities of cytokine production at birth. In vitro production of interleukin 2, interleukin 6 and interferon-gamma by peripheral blood mononuclear cells was measured in 53 newborns: 21 had cord blood IgE levels above 0.9 kU/l, 21 had a positive family history, 7 had both elevated IgE and a positive family history; 18 newborns with no identifiable risk for atopic disease served as controls. Umbilical cord blood mononuclear cells were stimulated with PHA or monoclonal antibody OKT3. In vitro production of interleukin 2 and 6 was comparable in all groups. Compared to controls IFN-gamma production of peripheral mononuclear cells (PBMC) from newborns with elevated cord blood IgE was not different, but PMBC from newborns with a familial risk showed a significant decrease in PHA induced IFN-gamma production (p < 0.005, U-test). No correlation between umbilical cord blood IgE and diminished IFN-gamma production was found in newborns with or without a positive family history. We conclude that immunoregulatory abnormalities in newborns of atopic families are detectable already at birth and are unrelated to cord blood IgE.

Recombinant interleukin-12 suppresses the synthesis of immunoglobulin E by interleukin-4 stimulated human lymphocytes

Interleukin-12 is a recently discovered lymphokine displaying an array of in vitro activities suggesting a major role in protective immunity against infectious agents like viruses. This study provides evidence that IL-12 may also be implicated in the selection of the immunoglobulin isotypes. We show that picomolar concentrations of rIL-12 markedly inhibit the synthesis of IgE by IL-4-stimulated PBMC. The suppression of IgE is observed at the protein and at the mRNA levels, it is isotype specific, and it is abolished by neutralizing anti-IL-12 mAbs. IL-12 may suppress IgE synthesis by: (a) inducing the production of IFN-gamma, a known inhibitor of IgE synthesis and (b) by a novel mechanism which is IFN-gamma independent. The best evidence for this is from studies on IgE synthesis by IL-4-plus hydrocortisone-stimulated umbilical cord blood lymphocytes, which do not produce detectable amounts of IFN-gamma. In such cultures, rIL-12 inhibits IgE synthesis even in the presence of a large excess of neutralizing anti-IFN-gamma mAb.

Cytokine-induced proliferation and immunoglobulin production of human B lymphocytes triggered through their CD40 antigen

Human resting B lymphocytes enter a state of sustained proliferation when incubated with both mouse fibroblastic L cells stably expressing Fc gamma RII/CDw32 and anti-CD40 antibodies. We have explored the effects of 11 recombinant human cytokines (CKs) on induced cell proliferation and immunoglobulin (Ig) production. Interleukin 4 (IL-4) was the only CK able to enhance anti-CD40-induced B cell multiplication as measured by enumeration of viable cells, and interferon gamma (IFN-gamma) further stimulated this induced proliferation. IL-4 enhanced the production of IgM and IgG by B cells and induced them to produce IgE. Combinations of IL-4 and IL-2 resulted in the production of large amounts of IgM and IgA. Interestingly, IFN-gamma did not inhibit the production of IgE by cells stimulated with anti-CD40 and IL-4. None of the tested CK combinations resulted in the production of large quantities of IgG. Therefore, this new culture system represents a unique model to study isotype regulation in highly purified human B lymphocytes, in addition to allowing the generation of long-term factor-dependent human B cell lines.

The in vivo expression of type B CD23 mRNA in B-chronic lymphocytic leukemic cells is associated with an abnormally low CD23 upregulation by IL-4: comparison with their normal cellular counterparts

We recently reported that the sera of chronic lymphocytic leukemia (CLL) patients contained 3-500 times more soluble CD23 (or IgE-BF) than the sera of patients with other lymphoproliferative diseases or normal individuals and that their B cells (B-CLLs) overexpressed CD23 Ag. In the present report, we extended these studies and showed that CD5+ B cells from all CLL patients (n = 15) co-express CD23 Ag. We next identified two additional major differences between B-CLLs and normal adult B cells. First, in contrast to normal adult B cells which exclusively express type A CD23 mRNA, freshly isolated B-CLLs expressed both type B and type A CD23 mRNA. Second, although IL-4 is a potent inducer of type B CD23 mRNA on normal B cells, an optimal concentration of IL-4 infranormally upregulated CD23 on highly purified B-CLLs both at the protein and at the molecular levels. However, co-stimulation of CLL PBMC with phytohemagglutinin (PHA) and IL-4 strongly upregulated CD23 on B-CLLs, reconstituting the high level of CD23 expression observed in vivo. We next attempted to relate B-CLLs to the CD5+ B cell subpopulations present in peripheral blood mononuclear cells (PBMC, n = 3), cord blood mononuclear cells (CBMC, n = 6) and tonsillar lymphocytes (TONS, n = 3) by analysing their co-expression of CD20, CD5 and CD23 Ag and their phenotypic regulation by IL-4. Our results indicated that B-CLLs presented some features in common with the CD23+ umbilical cord blood B cells in as much as, like in B-CLLs; (i) all CD23+ cord blood cells co-expressed CD5 Ag, (ii) freshly isolated CBMC expressed both type A and type B CD23 mRNA, and finally (iii) these cells weakly re-expressed CD23 Ag upon IL-4 stimulation as compared to adult PBMC.