Lysosomal dysfunction can result in endolysosomal storage disorders such as mucolipidoses or mucopolysaccharidoses but it is also implicated in development and progression of neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease, metabolic diseases, infectious diseases, retinal diseases and pigmentation disorders, trace metal deficiencies such as iron deficiency, and cancer. Highly critical for the proper function of lysosomes, endosomes, and lysosome-related organelles is the tight regulation of various fusion and fission processes and the regulation of proton, calcium and other cation concentrations within the endolysosomal system (ES). TRPML cation channels (TRPML1, 2 and 3) as well as two-pore channels (TPCs) have recently emerged as important regulators of such processes within the ES and appear to be essential for a proper communication between the various endolysosomal vesicles. We use endolysosomal patch-clamp techniques, molecular and cell biology techniques as well as genetic mouse models to study the physiological roles and activation mechanisms of these ion channels in-depth. While TRPML1 causes mucolipidosis type IV when lost or mutated, resulting in severe neuro- and retina degeneration, relatively little is known about the other two relatives, TRPML2 and TRPML3. Here, we present novel data relating to the physiological role of TRPML2 in the innate immune response. For the direct modulation of TRPML2 in endogenously expressing immune cells, we have developed a highly selective and potent agonist for TRPML2, ML2-SA1, which we applied and validated not only in endolysosomal patch clamp experiments, but also in a number of cellular assays to assess the role of TRPML2 in chemokine/cytokine release in more