B cells produce antibodies that target and mark pathogens—foreign invaders such as bacteria and viruses—for destruction. B cells detect these pathogens using structures on their surface called B-cell receptors (BCRs). Once triggered, BCRs instruct B cells to become plasma cells, which secrete antibodies.

In lupus, self-reactive B cells secrete autoantibodies that mistakenly target the body’s own cells and tissues, causing inflammation. BCR signaling is usually regulated by signaling inhibitors, which act like brakes to prevent B cells from becoming overactive. Multiple signaling inhibitor levels are reduced in people with SLE, but the reasons for this are unknown. Dr. Castrillon will study how signaling inhibitors are regulated in SLE, focusing on a specific inhibitor called CEACAM1.

Many cytokines produced by the immune system to fight viral infections are found at higher levels in people with lupus. The B cell activation threshold is lowered in the presence of these cytokines, meaning B cells are more likely to become activated.

Dr. Castrillon will compare signaling inhibitors’ levels in cells from healthy people and those with lupus. He will then test whether restoring these activation inhibitors in B cells from people with SLE can reduce their overactive state. To understand what alters inhibitors’ levels in SLE, Dr. Castrillon will expose B cells from healthy subjects to multiple activation-related cytokines and test whether this affects signaling inhibitor levels.

Lastly, he will assess whether patterns of signaling inhibitor levels in healthy individuals and those with active and inactive lupus correlate with their clinical features, such as demographics, SLEDAI score (a tool used to measure disease activity), and medical history.

What this means for people with lupus:
Dr. Castrillon’s findings will provide a detailed understanding of the molecules that cause B cells to become more easily activated in lupus. This knowledge could lead to the development of new strategies to classify and manage the conditions of people with lupus, potentially improving treatment and outcomes.

B cells are in a dysregulated hyperresponsive state in lupus, which leads to a lower threshold of activation for B cells that produce self-reactive autoantibodies. It is known that multiple B cell receptor (BCR) signaling inhibitors like FCGR2B and PTEN are downregulated in lupus patients in contrast to healthy donors. We have also identified that CEACAM1, a potential BCR signaling inhibitor, is also reduced in lupus patients B cells when compared to controls; we observed this specifically in the switched memory B cell compartment, which could have important repercussions in the perpetuation of self-reactive antibody specificities. The mechanism that leads to the downregulation of these proteins in lupus is largely unexplored. In this proposal, I will comprehensively profile BCR signaling inhibitors and explore their role in lupus clinical heterogeneity by integrating single cell transcriptomics, proteomics and antibody repertoire analysis of B cells with clinical information from lupus patients with different disease activity. In Aim 1, I will determine the molecular profile of B cells with different expression levels of signaling receptor inhibitors and I will test if restoring BCR signaling barriers can increase the activation threshold of B cells in lupus. In Aim 2, I will directly address if Interferon molecules are responsible for the barrier dysregulation of signaling inhibitors in B cells. Though it is well accepted the Interferon type 1 lowers the threshold of B cell activation, the precise molecular pathway has not been elucidated. We will fill this important gap in the biology of B cells in lupus. Through Aims 1 and 2, I will create a full characterization of B cells with distinct activation inhibition profiles, thereby establishing a foundational molecular blueprint for new potential therapeutic targets. In Aim 3, I will test if B cell receptor inhibitor profiles can be correlated to the clinical status of lupus patients. To achieve this, I will develop a comprehensive spectral flow cytometry panel to characterize cross-sectional and longitudinal donor samples from patients with active and inactive status and contrast their signaling inhibitor profile with their clinical information. With the execution of this proposal, I will answer two important questions in lupus: what mechanisms drive the downregulation of BCR signaling inhibitors and what does it mean to have an interferon signature for B cells. Moreover, this research will outline potential new therapeutic approaches that target B cells in lupus.