One theory on the etymology of 'April' is that this word derives from the Latin verb 'aperire', meaning 'to open', in tribute to the opening of flowers as spring begins. Fittingly, the theme of opening can apply to several articles in the April issue of Nature Reviews Immunology.

In our featured article (p251), David Schatz and Yanhong Ji explain how the genetic regions that encode antigen receptors are opened to enable DNA binding and cleavage by recombination activating gene (RAG) proteins. This is essential for V(D)J recombination; however, lymphoid malignancies can result when other genomic regions are inadvertently opened up to the RAGs.

On page 239, John O'Shea and colleagues describe the role of signal transducer and activator of transcription (STAT) proteins in keeping open (or closed) the genes that are key for different T cell functions. Such activity explains why specific STATs are associated with and crucial for the functions of distinct T cell lineages.

Can John Semple and colleagues persuade immunologists to open their eyes to an overlooked cell type? They discuss how platelets are not merely mediators of haemostasis, but can have important immunoregulatory functions. And should we open the door to fungi? Luigina Romani argues that maintaining friendly relations with these ubiquitous eukaryotes is crucial for avoiding fungal diseases; she explains the immune mechanisms that allow us to coexist in peace.

Finally, in our Perspective article on page 289, Arne Akbar and Sian Henson compare the mechanisms that regulate exhaustion and senescence in T cells. They argue that these are distinct processes, regulated independently of each other, and discuss the implications of this for developing immune-boosting therapies. And now ... time to open the issue!