Unique skin abnormality in patients with peanut allergy but no atopic dermatitis

BACKGROUND

The nonlesional skin of children with atopic dermatitis (AD) with peanut allergy (PA) is associated with increased transepidermal water loss; low urocanic acid (UCA) and pyrrolidone carboxylic acid (PCA), both of which are filaggrin breakdown products; and a reduced ratio of esterified ω-hydroxy fatty acid sphingosine ceramides (EOS-CERs) to nonhydroxy fatty acid sphingosine ceramides (NS-CERs) in the skin. The skin barrier of subjects with PA without AD (AD^-PA⁺) has not been studied.

OBJECTIVE

Our aim was to explore whether AD^-PA⁺ is associated with skin barrier abnormalities.

METHODS

A total of 33 participants were enrolled, including 13 AD^-PA⁺, 9 AD⁺PA⁺, and 11 nonatopic (NA) participants.

RESULTS

The PCA content in the stratum corneum of AD^-PA⁺ subjects was significantly reduced versus that in NA subjects (median level, 67 vs 97 μg/mg protein [P = .028]). The ratio between cis- and trans-UCA decreased significantly from being highest in the NA group (1.62) to lowest in AD⁺PA⁺ group (0.07 [P < .001 vs in the NA group; P = .006 vs in the AD^-PA⁺ group]), with the AD^-PA⁺ group having an intermediate cis/trans-UCA ratio (1.17 [P = .024 vs in the NA group]). The TEWL in AD^-PA⁺ subjects did not differ from that in the group with NA skin. Interestingly, AD^-PA⁺ subjects had an increased EOS/NS-CER ratio versus that in the group of subjects with NA skin (1.9 vs 1.3 [P = .008]), whereas the AD⁺PA⁺ group had a decreased proportion of EOS-CERs (0.8 [P = .001] vs in the AD^-PA⁺ group).

CONCLUSION

Our data demonstrate that irrespective of AD, PA is associated with decreased skin cis-UCA and PCA content. An increase in skin EOS-CER/NS-CER ratio separates the AD^-PA⁺ group from the AD⁺PA⁺ and NA groups.

Expansion of CD22lo B cells in the spleen of autoimmune-prone flaky skin mice

Similar to murine models with compromised CD22/SHP-1 function, flaky skin (fsn) mutant mice exhibit lymphocyte hyperactivation and an autoimmune phenotype characterized by circulating autoantibodies to dsDNA and glomerulonephritis. Immunophenotyping of fsn/fsn splenic B cells was performed to determine if abnormalities in CD22 expression contributed to the phenotype. We identified an expansion of an IgM(bright) CD22lo population consistent with immature B-lymphocytes. While normal B-lymphocytes require IL-4 to achieve down-modulation of CD22 expression in response to BCR cross-linking, culture with anti-IgM alone led to reduced CD22 expression in fsn/fsn mice. Furthermore, when IL-4 was added to fsn/fsn cultures, no further reduction in CD22 expression was observed. This suggested that fsn/fsn B cells were pre-activated in vivo by chronic IL-4 exposure. A portion of these CD22lo cells expressed the B-1 surface marker CD11b. We contend that decreased activation thresholds among CD22lo B-lymphocytes contributes to the expansion of immature and B-1 B cell populations and to the development of autoimmune pathology in fsn/fsn mice.

Lymphadenopathy, elevated serum IgE levels, autoimmunity, and mast cell accumulation in flaky skin mutant mice

The autosomal recessive mutation "flaky skin" (fsn) causes pleiotropic abnormalities in the immune and hematopoietic systems accompanied by pathologic changes in the skin. Homozygotes (fsn/fsn) showed increased size and histological alterations in the spleen and lymph nodes. Abnormalities in lymphoid architecture of the spleen in fsn/fsn mice were accompanied by marked increases in total numbers of B cells, macrophages, and immature erythroid cells. Splenic B cells displayed elevated MHC class II expression. Serum IgE levels were greater than 100 microg/ml by 10 weeks of age, representing > 7000-fold increase compared with normal littermates. This increased IgE level was associated with elevated IL-4 production by spleen cells and with increased amounts of serum IL-4. Serum IgM, IgG1, and IgG2b levels were also increased in fsn/fsn mice while IgG3 was decreased. Autoimmunity in fsn/fsn mice was evidenced by glomerulonephritis accompanied by immune complex deposition in the kidneys, increased serum blood urea nitrogen levels, and the presence of circulating anti-double-stranded DNA autoantibodies. Pathological changes in the skin of fsn/fsn mice were characterized by epidermal hyperplasia and mixed dermal inflammation. Increased numbers of mast cells were also observed in the dermis of the truncal skin as well as in the epithelial stomach. These marked immunological abnormalities suggest that the fsn locus encodes a major immunoregulatory molecule important in multiple immune and hematopoietic functions.