The round, in which four venture capitalist funds participated, raised €18 million (£16 million) to support clinical trials targeting inflammatory diseases such as lupus and rheumatoid arthritis.
As part of the financing, Florent Gros, managing director at early-stage healthcare investor Novartis Venture Fund, and Dr Manus Rogan, managing partner at Dublin-based Fountain Healthcare Partners, will join the board of directors.
The other two firms named as investors in the round are life sciences investor Inventages Venture Capital and Seroba Kernel Life Sciences, which has offices in Ireland and the UK.
Opsona has also announced the opening of a new laboratory in Switzerland.