Figure 1.

Development of zebrafish immunity in comparison with the human immune system. Zebrafish possess a complex immune system, similar to that of humans. Development of zebrafish larvae is shown in A and a time line is shown in B. The appearance of components of the immune system is shown in C, and comparison is made with human immune components. Components of the innate immune system are detectable and active in the first days postfertilization (dpf) (e.g., macrophages, neutrophils, eosinophils, and mast cells). Adaptive immunity takes longer to develop and starts with thymus development at 60 hours postfertilization (hpf) and the appearance of the first lymphocytic markers at ∼4 dpf. At 21 dpf, the thymus is fully matured, and the first mature T cells and B cells are detected; humoral immunity is functional at 28 dpf. wpf, weeks postfertilization; TCR, T-cell receptor; NK, natural killer; MHC, major histocompatibility complex; DC, dendritic cell; APC, antigen-presenting cell; TLR, Toll-like receptor; NITR, novel immune-type receptor; TNF-α, tumor necrosis factor-α; IFN, interferon. References cited in figure as follows: a, Herbomel et al. 1999; b, Herbomel et al. 2001; c, Traver et al. 2003; d, Meijer and Spaink 2011; e, Novoa and Figueras 2012; f, Renshaw et al. 2006; g, Le Guyader et al. 2008; h, Renshaw and Trede 2012; i, Bertrand et al. 2007; j, Balla et al. 2010; k, Meeker and Trede 2008; l, Dobson et al. 2008; m, Lam et al. 2002; n, Trede et al. 2004; o, Danilova et al. 2004; p, Schorpp et al. 2006; q, Meeker et al. 2010; r, Laing and Hansen 2011; s, Lam et al. 2004; t, Danilova et al. 2005; u, Page et al. 2013; v, Yoder 2009; w, Yoder et al. 2010; x, van der Sar et al. 2004b; y, van der Vaart et al. 2012; z, Palha et al. 2013; aa, de Jong et al. 2011; bb, de Jong and Zon 2012; cc, Lugo-Villarino et al. 2010.