3.2. Distinct microbial signatures of SAC/PAC and VKC
Apart from the differences in manifestation and incidence, SAC/PAC and VKC are driven by different immune reactions. Previous studies suggested VKC are mainly related to Th2-type allergic inflammation while SAC/PAC manifest the classical type I hypersensitivity.30 In addition, type IV hypersensitivity is involved in VKC. We thus asked whether the conjunctival microbiota was different between SAC/PAC and VKC. Although the alpha diversity of the entire AC group showed no difference to the healthy group, the conjunctival microbiota of the patients with SAC/PAC was less diverse than healthy subjects (Figure 4A;P = 0.043). We did not find significant difference in inter-individual variation within samples of SAC/PAC and VKC (Figure 4B;P = 0.31). As expected, the species composition of conjunctival microbiome distinguished between SAC/PAC and VKC (Figure 4C). We then performed linear discriminant analysis to identify the species signatures of SAC/PAC and VKC (Figure 4D).
The distribution of species that showed differences in abundance between SAC/PAC and VKC were summarized in Figure 5A. Brevibacterium aurantiacum was enriched in SAC/PAC (Figure 5B; Kruskal-Wallis rank-sum test P = 0.0062). We observed the enrichment ofStreptococcus species in VKC (Figure 5C), includingStreptococcus pneumoniae (P = 0.033), Streptococcus salivarius (P = 0.022), and Streptococcus sanguinis(P = 0.034). Haemophilus parainfluenzae (P = 0.041), Actinomyces sp . oral taxon 848 (P = 0.026), andCampylobacter concisus (P = 0.013) were also more abundant and more prevalent in VKC compared with SAC/PAC. Colonization ofS. pneumoniae and Haemophilus Influenzae in airways are also the risk factors of asthma.28Campylobacter in lower airways is associated with resistance to corticosteroids in asthma.31 Interesting, alpha-hemolytic Streptococcus (which includes S. pneumoniae and S. sanguinis ) and H. Influenzae were observed on the ocular surface of oGVHD patients using culture-based methods.32 These results indicate that the composition of conjunctival microbiota is associated with specific types of AC, which potentially provides novel aspects for the prevention and treatment of ocular allergy.