Abstract The glycocalyx surrounding leukocytes has been studied for its role in immunomodulation and its potential as a therapeutic target. 4-methylumbelliferone (4MU) is a small molecule that inhibits production of the glycocalyx’s primary polysaccharide component hyaluronan (HA), by targeting the HA synthase (HAS). Oral treatment with 4MU has proved efficacious in preventing the development and progression of autoimmunity, though the mechanism is contested. We have previously shown that 4MU strongly inhibits T-cell mediated autoimmunity, and report here that it also attenuates formation of antigen-specific plasmablasts and subsequent autoantibody production. This suggests that the HA glycocalyx plays a role in promoting the humoral component of autoimmunity. The HAS proteins are deeply membrane embedded, preventing the use of traditional flow cytometry antibodies to define expression levels across leukocyte compartments. This limitation has made it difficult to identify cellular targets of 4MU. Alternative measurements must be used to study the HA glycocalyx. Surface HA content of a cell can be measured with labelled HA binding protein (HABP), though this does not explain whether HA was synthesized or scavenged with HA-binding receptors. RNA measurement can also be used to look at transcript levels of the HAS proteins. Here, we combine RNA in situ hybridization, fluorescently labeled HA binding protein (HABP), and conventional flow cytometry antibodies to define the HA glycocalyx on leukocytes during autoimmunity. Utilizing Spectral Flow Cytometry, we can assess parameters in numbers comparable to Mass Cytometry (CyTOF) to identify which cells are most likely targeted by 4MU to prevent antibody formation during autoimmunity.