Acts as a positive regulator of T-cell maturation and inflammatory function. Required for several functions of T-cells, in both the CD4(+) and the CD8(+) compartments and this includes expression of cell surface markers of activation, proliferation, and cytokine production in response to specific or non-specific stimulation (By similarity). Enhances NK cell cytotoxicity by positively regulating polarization of microtubule-organizing center (MTOC) to cytotoxic synapse, lytic granule transport along microtubules, and dynein- mediated clustering to MTOC (PubMed:25762780). Interacts with HSPA5 and stabilizes the interaction between HSPA5 and ERN1, leading to suppression of ERN1-induced JNK activation and endoplasmic reticulum stress-induced apoptosis (PubMed:21289099). {ECO:0000250|UniProtKB:Q4QRL3, ECO:0000269|PubMed:21289099, ECO:0000269|PubMed:25762780}. This is the function of CCDC88B (coiled-coil and HOOK domain protein 88B, Ensembl gene identifier ENSG00000168071).