The Major Cow Milk Allergen Bos d 5 Manipulates T-Helper Cells Depending on Its Load with Siderophore-Bound Iron

Abstract

The mechanisms of allergic sensitization to milk are still elusive. The major allergen Bos d 5 belongs to the lipocalin-family and thus is able to transport numerous ligands. In this study we investigated its ability to bind to iron-siderophore complexes and tested the immune-modulatory properties of Bos d 5 in either forms. Structural and in silico docking analysis of Bos d 5 revealed that Bos d 5 is able to bind to iron via catechol-based flavonoids (quercetin, myricetin, luteolin) that act as siderophores as confirmed by spectral-analysis and iron staining. Calculated dissociation constants of docking analyses were below 1 µM by virtual addition of iron. When incubated with human peripheral blood mononuclear cells (PBMCs), only the apo-form of Bos d 5 led to an increase of CD4+positive cells and significantly elevated IL13 and IFNγ-levels. In contrast, holo-Bos d 5 decreased numbers of CD4 expressing cells and induced apoptosis. Taken together, our data give evidence that Bos d 5 is capable of binding iron via siderophores. Moreover, our data support for the first time the notion that the form of application (apo- or holo-form) is decisive for the subsequent immune response. The apo-form promotes Th2 cells and inflammation, whereas the holo-form appears to be immunosuppressive.

Allergenic Can f 1 and its human homologue Lcn‐1 direct dendritic cells to induce divergent immune responses

“…40 found immunomodulatory activity of hard tick-derived lipocalins and Roth-Walter et al . found that the lipocalin cow allergen holo-Bos d 5 and the lipocalin-like holo-Bet v2 promote Th2 cells 41,42. In our study we confirm DC-modulatory activity by a second pair of homologous lipocalins, the cat dander allergen Fel d 4 and its putative human homologue MUP.…”

“…Although most of the data shown in these reports are not directly comparable to our study, some are still contradictory. Virtanen and colleagues found that mammalian lipocalin allergens do not exhibit DC-activating capacity and found no differences in the CD4 + T cell responses to the two homologous lipocalins [38,39] while Preston et al [40] found immunomodulatory activity of hard tick-derived lipocalins and Roth-Walter et al found that the lipocalin cow allergen holo-Bos d 5 and the lipocalin-like holo-Bet v2 promote Th2 cells [41,42]. In our study we confirm DC-modulatory activity by a second pair of homologous lipocalins, the cat dander allergen Fel d 4 and its putative human homologue MUP.…”

Probing the modulated formation of gold nanoparticles–beta-lactoglobulin corona complexes and their applications

“…Oral administration of certain sized AuNPs did not produce observable systemic toxicities 18 and only a tiny amount of oral dose would be absorbed and retained in the body 19 . β-LG, the major whey protein component in cow’s milk, is an 18.4 kDa protein with 162 residues involved in molecular transport and immune modulation 20–21 . β-LG is a clinically critical antigen associated to milk allergy and plays an indispensable role in vaccination and oral tolerance induction 22–23 .…”

Structural similarities of human and mammalian lipocalins, and their function in innate immunity and allergy

“…More importantly, the load of this binding pocket is decisive for the immunomodulatory function of lipocalins. Only the apo‐form of lipocalin Bos d 5 and lipocalin‐like allergen Bet v 1 promoted the survival of CD4+ T cells and IL‐13 production in human PBMCs, whereas the holo‐form was nonallergenic, so far at least in vitro . Consistent with this function, the loading state of brain lipocalin is decisive for the survival of neuronal cells .…”

“…The known anti‐bacterial activity of the human neutrophil lipocalin LCN2 (NGAL) is caused by the high affinity of this lipocalin for the siderophore‐Fe3+ complex and it should be investigated systematically whether from this it can be extrapolated to animal lipocalins. In fact, the molecular ligand transport function of lipocalins and of lipocalin‐like proteins could be particularly significant for the Th2 skewing capacity, independent of their mammalian or plant origin. We propose that this feature is likely connected with the similar β‐barrel fold in human and animal lipocalins (Fig.…”