Elaine Agius

Different Proliferative Potential and Migratory Characteristics of Human CD4+ Regulatory T Cells That Express either CD45RA or CD45RO

Although human naturally occurring regulatory T cells (Tregs) may express either CD45RA or CD45RO, we find in agreement with previous reports that the (∼80%) majority of natural Tregs in adults are CD45RO+. The proportion of CD45RA+ Tregs decreases, whereas CD45RO+ Tregs increase significantly with age. Nevertheless, a small proportion of CD45RA+ Tregs are found even in old (>80 y) adults and a proportion of these express CD31, a marker for recent thymic emigrants. We found that CD45RO+ Tregs were highly proliferative compared with their CD45RA+ counterparts. This was due in part to the conversion of CD45RA Tregs to CD45RO expression after activation. Another difference between these two Treg populations was their preferential migration to different tissues in vivo. Whereas CD45RA+ Tregs were preferentially located in the bone marrow, associated with increased CXCR4 expression, CD45RO+ Tregs were preferentially located in the skin, and this was associated with their increased expression of CLA and CCR4. Our studies therefore show that proliferation features strongly in maintenance of the adult Treg pool in humans and that the thymus may make a minor contribution to the maintenance of the peripheral pool of these cells, even in older adults. Furthermore, the different tissue compartmentalization of these cells suggests that different Treg niches exist in vivo, which may have important roles for their maturation and function.

The kinetics of CD4 + Foxp3 + T cell accumulation during a human cutaneous antigen-specific memory response in vivo

Naturally occurring CD4(+)CD25(hi)Foxp3(+) Tregs (nTregs) are highly proliferative in blood. However, the kinetics of their accumulation and proliferation during a localized antigen-specific T cell response is currently unknown. To explore this, we used a human experimental system whereby tuberculin purified protein derivative (PPD) was injected into the skin and the local T cell response analyzed over time. The numbers of both CD4(+)Foxp3(-) (memory) and CD4(+)Foxp3(+) (putative nTreg) T cells increased in parallel, with the 2 populations proliferating at the same relative rate. In contrast to CD4(+)Foxp3(-) T cell populations, skin CD4(+)Foxp3(+) T cells expressed typical Treg markers (i.e., they were CD25(hi), CD127(lo), CD27(+), and CD39(+)) and did not synthesize IL-2 or IFN-gamma after restimulation in vitro, indicating that they were not recently activated effector cells. To determine whether CD4(+)Foxp3(+) T cells in skin could be induced from memory CD4(+) T cells, we expanded skin-derived memory CD4(+) T cells in vitro and anergized them. These cells expressed high levels of CD25 and Foxp3 and suppressed the proliferation of skin-derived responder T cells to PPD challenge. Our data therefore demonstrate that memory and CD4(+) Treg populations are regulated in tandem during a secondary antigenic response. Furthermore, it is possible to isolate effector CD4(+) T cell populations from inflamed tissues and manipulate them to generate Tregs with the potential to suppress inflammatory responses.

Decreased TNF-α synthesis by macrophages restricts cutaneous immunosurveillance by memory CD4+ T cells during aging

Immunity declines during aging, however the mechanisms involved in this decline are not known. In this study, we show that cutaneous delayed type hypersensitivity (DTH) responses to recall antigens are significantly decreased in older individuals. However, this is not related to CC chemokine receptor 4, cutaneous lymphocyte-associated antigen, or CD11a expression by CD4+ T cells or their physical capacity for migration. Instead, there is defective activation of dermal blood vessels in older subject that results from decreased TNF-α secretion by macrophages. This prevents memory T cell entry into the skin after antigen challenge. However, isolated cutaneous macrophages from these subjects can be induced to secrete TNF-α after stimulation with Toll-like receptor (TLR) 1/2 or TLR 4 ligands in vitro, indicating that the defect is reversible. The decreased conditioning of tissue microenvironments by macrophage-derived cytokines may therefore lead to defective immunosurveillance by memory T cells. This may be a predisposing factor for the development of malignancy and infection in the skin during aging.

Varicella Zoster–Specific CD4+Foxp3+ T Cells Accumulate after Cutaneous Antigen Challenge in Humans

We investigated the relationship between varicella zoster virus (VZV)–specific memory CD4+ T cells and CD4+Foxp3+ regulatory T cells (Tregs) that accumulate after intradermal challenge with a VZV skin test Ag. VZV-specific CD4+ T cells were identified with a MHC class II tetramer or by intracellular staining for either IFN-γ or IL-2 after Ag rechallenge in vitro. VZV-specific T cells, mainly of a central memory (CD45RA−CD27+) phenotype, accumulate at the site of skin challenge compared with the blood of the same individuals. This resulted in part from local proliferation because >50% of tetramer defined Ag-specific CD4+ T cells in the skin expressed the cell cycle marker Ki67. CD4+Foxp3+ T cells had the characteristic phenotype of Tregs, namely CD25hiCD127loCD39hi in both unchallenged and VZV challenged skin and did not secrete IFN-γ or IL-2 after antigenic restimulation. The CD4+Foxp3+ T cells from unchallenged skin had suppressive activity, because their removal led to an increase in cytokine secretion after activation. After VZV Ag injection, Foxp3+CD25hiCD127loCD39hi T cells were also found within the VZV tetramer population. Their suppressive activity could not be directly assessed by CD25 depletion because activated T cells in the skin were also CD25+. Nevertheless, there was an inverse correlation between decreased VZV skin responses and proportion of CD4+Foxp3+ T cells present, indicating indirectly their inhibitory activity in vivo. These results suggest a linkage between the expansion of Ag-specific CD4+ T cells and CD4+ Tregs that may provide controlled responsiveness during Ag-specific stimulation in tissues.

The Characterization of Varicella Zoster Virus-Specific T Cells in Skin and Blood during Aging

Reactivation of the varicella zoster virus (VZV) increases during aging. Although the effects of VZV reactivation are observed in the skin (shingles), the number and functional capacity of cutaneous VZV-specific T cells have not been investigated. The numbers of circulating IFN-γ-secreting VZV-specific CD4(+) T cells are significantly decreased in old subjects. However, other measures of VZV-specific CD4(+) T cells, including proliferative capacity to VZV antigen stimulation and identification of VZV-specific CD4(+) T cells with an major histocompatibility complex class II tetramer (epitope of IE-63 protein), were similar in both age groups. The majority of T cells in the skin of both age groups expressed CD69, a characteristic of skin-resident T cells. VZV-specific CD4(+) T cells were significantly increased in the skin compared with the blood in young and old subjects, and their function was similar in both age groups. In contrast, the number of Foxp3(+) regulatory T cells and expression of the inhibitory receptor programmed cell death -1 PD-1 on CD4(+) T cells were significantly increased in the skin of older humans. Therefore, VZV-specific CD4(+) T cells in the skin of older individuals are functionally competent. However, their activity may be restricted by multiple inhibitory influences in situ.

Dermojet delivery of bleomycin for the treatment of recalcitrant plantar warts.

Background: Plantar warts may cause significant morbidity. Intralesional bleomycin is effective. When bleomycin is injected with a needle and syringe, it is difficult to prevent the bleomycin from infiltrating the dermis adjacent to the wart, producing unnecessary acute pain, persistent pain, and potential sloughing of normal adjacent skin. Efficacy of delivery by dermojet is not yet established. Objectives: To assess the response of recalcitrant plantar warts to bleomycin delivered by dermojet. Methods: A total of 47 patients with 138 plantar warts present for more than 2 years and resistant to 10 cycles of cryosurgery, were recruited. Bleomycin (1 U/ml) was delivered intralesionally by dermojet at 5‐week intervals for 25 weeks. Results: Out of 138, 124 (89.9%) plantar warts showed complete or partial clearance after one to five sets of bleomycin injections. The recurrence rate was 6/138 (4.4%), and 8/138 (5.8%) warts failed to clear. The reduction in mean surface area of the plantar warts after each set of bleomycin injections compared to baseline surface area was statistically significant. Local side effects were similar to other methods of delivery. No systemic side effects were reported. Conclusions: This study assesses therapeutic efficacy of bleomycin delivered by dermojet in solely recalcitrant plantar warts. It provides preliminary evidence that this method of delivery may benefit a group of patients with particularly recalcitrant plantar warts and is safe and easy to use in routine dermatology practice.

Enhancement of cutaneous immunity during ageing by blocking p38 MAPkinase induced inflammation

Background Immunity decreases with age, which leads to reactivation of varicella zoster virus (VZV). In human subjects age‐associated immune changes are usually measured in blood leukocytes; however, this might not reflect alterations in tissue‐specific immunity. Objectives We used a VZV antigen challenge system in the skin to investigate changes in tissue‐specific mechanisms involved in the decreased response to this virus during aging. Methods We assessed cutaneous immunity based on the extent of erythema and induration after intradermal VZV antigen injection. We also performed immune histology and transcriptomic analyses on skin biopsy specimens taken from the challenge site in young (<40 years) and old (>65 years) subjects. Results Old human subjects exhibited decreased erythema and induration, CD4+ and CD8+ T‐cell infiltration, and attenuated global gene activation at the site of cutaneous VZV antigen challenge compared with young subjects. This was associated with increased sterile inflammation in the skin in the same subjects related to p38 mitogen‐activated protein kinase–related proinflammatory cytokine production (P < .0007). We inhibited systemic inflammation in old subjects by means of pretreatment with an oral small‐molecule p38 mitogen‐activated protein kinase inhibitor (Losmapimod; GlaxoSmithKline, Brentford, United Kingdom), which reduced both serum C‐reactive protein levels and peripheral blood monocyte secretion of IL‐6 and TNF‐&agr;. In contrast, cutaneous responses to VZV antigen challenge were increased significantly in the same subjects (P < .0003). Conclusion Excessive inflammation in the skin early after antigen challenge retards antigen‐specific immunity. However, this can be reversed by inhibition of inflammatory cytokine production that can be used to promote vaccine efficacy and the treatment of infections and malignancy during aging. Graphical abstract Figure. No Caption available.