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Skin sensitization: Langerhans’ cell mobilization, cytokine regulation and immunomodulation by lactoferrin.
[Thesis]. Manchester, UK: The University of Manchester; 2015.
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Abstract
Allergic contact dermatitis is an important occupational health disease. It represents a useful experimental paradigm in which the mechanisms and characteristics of cutaneous immune responses can be investigated. This thesis has focused on the sensitization phase of contact allergy, including Langerhans’ cell (LC) migration, cytokine expression and the ability of the protein lactoferrin (LF) to modulate aspects of these processes. Lactoferrin was originally identified as an antimicrobial protein. However, it is being recognized increasingly to have immunomodulatory effects on the cells of the immune system. Migration of LC in mice and in humans is mediated via two independent cytokine signals delivered by tumour necrosis factor (TNF)-α and interleukin (IL)-1β, which were thought to derive from keratinocytes and LC, respectively. Further, topical application of LF was shown to inhibit LC migration in both man and mouse potentially through the inhibition of de novo TNF-α production.The inhibitory effect of LF on LC mobilization induced by the contact allergen 4-ethoxymethylene-2-phenyl-2-oxazolin-5-one (oxazolone) has been confirmed in these investigations. Conversely, LF did not inhibit LC migration triggered by another contact allergen, 2,4-dinitrochlorobenzene (DNCB). That result prompted a comparison between oxazolone and DNCB with respect to their ability to induce LC migration and to provoke cutaneous cytokine production. It was discovered that DNCB induced LC mobilization in the absence of TNF-α signalling. Moreover, exposure to superoptimal doses of oxazolone resulted in TNF-α independent LC migration. Further experiments revealed that TNF-α independence might be mediated partially by the elevated concentration of IL-1β produced in the skin following exposure to DNCB and these superoptimal concentrations of oxazolone.Investigations of the immunomodulatory mechanism of LF in vitro demonstrated that it did not inhibit TNF-α production by THP-1 macrophages. On the contrary, LF was shown to stimulate TNF-α and IL-8 release by THP-1 macrophages in a dose dependent manner, via endotoxin-independent and nucleolin-dependent mechanism. Subsequently, the role of LF in modulation of keratinocyte activation was investigated. Keratinocytes expressed high levels of inducible TNF-α mRNA, however, this was not modulated specifically by LF. Additional examination of the effects of LF in vivo revealed that it inhibited cutaneous IL-17 and CXCL1 mRNA expression, induced by IL-1β and IL-1α, respectively. Lactoferrin treatment did not affect oxazolone-induced lymph node (LN) cell proliferation. However, it was demonstrated to decrease IL-17 production by LN cells 24h following exposure to oxazolone, which may be important in driving the vigour and/or quality of response to the contact allergen.Overall, these investigations have demonstrated a divergence within the family of contact allergens with regard to the requirement for TNF-α signalling for LC mobilization. It was established that when elevated concentrations of IL-1β are present LC migration can occur in the absence of TNF-α signalling. Moreover, a dual nature of LF, which can act in a stimulatory as well as inhibitory manner, was confirmed. These investigations have revealed a potential role for CXCL1 and IL-17 in the process of LC migration. Furthermore, it was shown that the inhibitory effect of LF on oxazolone induced LC migration might be mediated via its effect on IL-17.