AIM: To assess the efficacy of topical Semaphorin 3A(SEMA3A) in the treatment of allergic conjunctivitis.METHODS: Experimental allergic conjunctivitis(EAC)mice model induced by short ragweed pollen(SRW) in 4-week-old of BALB/c mice, mice were evaluated using haematoxylin and eosin(H&E) staining, immunofluor-escence and light microscope photographs. Early phase took the samples in 24 h after instillation and late phase took the samples between 4 to 14 d after the start of treatment. The study use of topical SEMA3A(10 U, 100 U,1000 U) eye drops and subconjunctival injection of SEMA3 A with same concentration. For comparison, five types of allergy eyedrops were quantified using clinical characteristics.· RESULTS: Clinical score of composite ocular symptoms of the mice treated with SEMA3 A were significantly decreased both in the immediate phase and the late phase compared to those treated with commercial ophthalmic formulations and non-treatment mice. SEMA3 A treatment attenuates infiltration of eosinophils entering into conjunctiva in EAC mice. The score of eosinophil infiltration in the conjunctiva of SEMA3 A 1000 U-treated group were significantly lower than low-concentration of SEMA3 A treated groups and non-treated group. SEMA3 A treatment also suppressed T-cell proliferation in vitro and decreased serum total Ig E levels in EAC mice. Moreover, treatment of SEMA3 A suppressed Th2-related cytokines(IL-5, IL-13 and IL-4)and pro-inflammatory cytokines(IFN-γ, IL-17 and TNF-α)release, but increased regulatory cytokine IL-10 concentration in the conjunctiva of EAC mice.CONCLUSION: SEMA3 A as a biological agent, showed the beneficial activity in ocular allergic processes with the less damage to the intraocular tissue. It is expected that SEMA3 A may be contributed in patients with a more severe spectrum of refractory ocular allergic diseases including allergic conjunctivitis in the near future. AIM: To assess the efficacy of topical Semaphorin 3A (SEMA3A) in the treatment of allergic conjunctivitis. METHODS: Experimental allergic conjunctivitis (EAC) mice model induced by short ragweed pollen (SRW) in 4-week-old of BALB / c mice, mice were evaluated using haematoxylin and eosin (H & E) staining, immunofluor-escence and light microscope photographs. of topical SEMA3A (10 U, 100 U, 1000 U) eye drops and subconjunctival injection of SEMA3 A with same concentration. For comparison, five types of allergy eyedrops were quantified using clinical characteristics. RESULTS: Clinical score of composite ocular symptoms of the mice treated with SEMA3 A were significantly decreased both in the immediate phase and the late phase compared to those treated with commercial ophthalmic formulations and non-treatment mice. SEMA3 A treatment attenuates infiltr ation of eosinophils entering into conjunctiva in EAC mice. The score of eosinophil infiltration in the conjunctiva of SEMA3 A 1000 U-treated group were significantly lower than low-concentration of SEMA3 A treated groups and non-treated group. SEMA3 A treatment also suppressed T -cell proliferation in vitro and decreased serum total Ig E levels in EAC mice. Moreover, treatment of SEMA3 A suppressed Th2-related cytokines (IL-5, IL- 13 and IL- 4) and pro- inflammatory cytokines IL-17 and TNF-α) release, but increased regulatory cytokine IL-10 concentration in the conjunctiva of EAC mice. CONCLUSION: SEMA3 A as a biological agent, showed the beneficial activity in ocular allergic processes with the less damage to the intraocular tissue It is expected that SEMA3 A may be contributed in patients with a more severe spectrum of refractory ocular allergic diseases including allergic conjunctivitis in the near future.