Insights into the clinical and immunological significance of anti-α-fodrin antibodies in systemic lupus erythematosus

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Dear Editor,

Alpha (α)-fodrin, a non-erythroid homolog of spectrin, plays a role in maintaining the structural stability of cell membranes. During apoptosis, α-fodrin undergoes enzymatic cleavage by caspase-3, generating smaller fragments that act as neoantigens.^[1]^ Anti-α-fodrin antibodies are found in autoimmune disorders, including primary Sjögren’s syndrome (70%) and systemic lupus erythematosus (SLE; 10%–30%), as well as in a minority of healthy individuals (~2%).^[2,3]^ Experimental studies in animal models have demonstrated that immunization with α-fodrin induces lympho-cytic infiltration in salivary glands, while immunization with human Ro antigen results in the production of anti-α-fodrin antibodies, suggesting a potential shared intermolecular epitope between Ro and α-fodrin.^[4,5]^ However, the association between anti-α-fodrin antibodies and SLE-related clinical or immunological manifestations remains insufficiently investigated and is often overlooked in studies where SLE patients serve only as controls.

Our study aimed to elucidate the association between anti-α-fodrin antibodies and clinical as well as immunological perturbations in SLE, particularly their relationship with anti-Ro/anti-Ro52 antibodies and chemokine levels.

The study was approved by the local ethics committee (protocol number 16–960) and participants provided written informed consent. Thirty adult SLE patients (86% female; median age: 41 [19–63] years) without sicca symptoms, xero-stomia, xerophthalmia, or Sjögren’s syndrome participated in the study. Disease activity was assessed using the systemic lupus erythematosus disease activity index-2000 (SLEDAI-2K) score, with organ involvement categorized based on predefined criteria detailed elsewhere.^[6]^ Anti-α-fodrin IgA and IgG antibodies (cut-off ≥10 U/mL), as well as anti-Ro and an-ti-Ro52 antibodies (≥25 U/mL) (Orgentec; Mainz, Germany), were measured by Enzyme linked immunosorbent assay (ELISA). Positivity for anti-α-fodrin antibodies was defined by the detection of either IgA or IgG antibodies. Serum chemo-kines were measured using multiplexed bead-based assays (ThermoFisher Scientific; Minneapolis, United States).

Six patients tested positive for anti-α-fodrin IgA antibodies, while two tested positive for anti-α-fodrin IgG antibodies. Table 1 summarizes the main clinical and laboratory findings. No significant differences in demographics, comorbidities, disease severity, organ involvement, or medication usage were observed between antibody-positive and antibody-negative patients. Similarly, there were no differences in serum positivity for other SLE-associated antibodies. Median levels of anti-Ro (0, 3–35 U/mL vs. 0, 0–108 U/mL; P = 0.47) and anti-Ro52 (0, 0–21 U/mL vs. 0, 0–97 U/mL; P = 0.86) antibodies were similar between the groups.

The median levels of anti-α-fodrin IgA antibodies were 2.8 (0–34.3) U/mL, and for IgG antibodies, the median was 2.2 (0–14.0) U/mL (Figure 1–A). Disease activity analysis indicated that 26% of patients had quiescent disease, 66% had mild to moderate activity, and 6% had high activity. Nonetheless, no correlation was observed between SLEDAI-2K scores and anti-α-fodrin IgA (Spearman’s rho-0.02 [-0.39 to 0.34]; P = 0.89. Figure 1–B) or IgG (rho-0.04 [-0.40 to 0.33]; P = 0.81. Figure 1–E) antibody titers.

Chemokine analysis revealed that anti-α-fodrin-positive patients exhibited lower levels of C-C motif ligand 11 (CCL11)/eotaxin (54, 30–132 ng/L vs. 91, 23–339 ng/L; P = 0.02) and C-C motif ligand 2 (CCL2)/monocyte chemoattractant protein 1 (MCP-1) (136, 36–394 vs. 379, 107–2211 ng/L; P < 0.01) compared to antibody-negative patients. Other chemokine levels were similar between the groups (Table 1). Furthermore, levels of anti-α-fodrin immunoglobulin (IgA) antibodies were inversely correlated with CCL11/eotaxin (rho-0.38 [-0.66 to-0.02]; P = 0.03. Figure 1–C) and CCL2/MCP-1 (rho-0.39 [-0.66 to-0.03]; P = 0.02. Figure 1–D). Conversely, anti-α-fodrin IgG antibodies showed no significant correlation with CCL11/eotaxin (rho-0.32 [-0.62 to 0.04]; P = 0.07. Figure 1–F) or CCL2/MCP-1 (rho-0.03 [-0.39 to 0.34]; P = 0.86. Figure 1–G).

This study provides novel insights into the clinical and immunological roles of anti-α-fodrin antibodies in SLE. Contrary to initial expectations, no significant associations were observed between anti-α-fodrin antibodies and disease severity, organ involvement, or anti-Ro/anti-Ro52 antibodies in SLE patients. These findings contrast with animal models of Sjögren’s syndrome, where a connection between anti-α-fodrin and anti-Ro antibodies has been suggested.^[4,5,7]^ Interestingly, our findings reveal a potential link between anti-α-fodrin antibodies and reduced levels of certain chemokines, suggesting a possible protective role in modulating the inflammatory response triggered by α-fodrin-induced apoptosis. This mechanism aligns with other cases of antibody-mediated regulation of harmful proteins in SLE, such as anti-cytokine autoantibodies that neutralize excessive cytokine activity and mitigate tissue damage.^[8]^ A plausible mechanism is that anti-α-fodrin antibodies may sequester free α-fodrin, preventing its activation of caspase-3 and subsequent apoptosis. This could reduce the production of chemokines like CCL2/MCP-1 and CCL11/eotaxin, which are crucial for recruiting immune cells such as monocytes and granulocytes.^[9,10]^

Although the small sample size and cross-sectional design limit the ability to draw definitive conclusions, our study failed to establish a clear association between anti-α-fodrin antibodies and anti-Ro/anti-Ro52 antibodies, disease severity, or organ-specific involvement in SLE. Nevertheless, our findings suggest a potential mechanistic role for these antibodies in regulating chemokine-driven inflammation.