Lymph clotting in LDLNs correlates with intralymphatic NETs in the LDLN and neutrophil load in the lungs of COVID-19 decedents. (A) Representative tiled immunofluorescence image of COVID-19 LDLN showing NETs (citrullinated histone 3 [H3cit], red) integrated into fibrin clots (green) within a large lymphatic vessel (podoplanin, blue) near the subcapsular sinus. (B) Percentage of clotted (fibrin score 3-4) or open (fibrin score 0-2) lymphatic vessels that contain NETs in LDLNs from control (red), COVID-19 (black), and H1N1 (blue) decedents. Dashed line represents the median for each group, and dotted lines represent the first and third quartiles. ∗∗P < .01 by two-tailed paired Student t test. (C-D) Correlation of average NET score (rubric shown in supplemental Figure 3) with percentage of clotted lymphatic vessels (C) and GC abnormality score (D) in each LDLN. (E) Representative tiled immunofluorescence images from lung (left) and matching LDLN (right) from 2 different patients with COVID-19 showing relationship between neutrophil density in the lung with lymphatic clotting and intralymphatic NETs in the LDLN. In patient A (top), a low density of neutrophils and NETs (MPO, yellow; H3cit, red) in the lung (left) corresponded to an LDLN (right) with mostly open lymphatic vessels (fibrin, green; podoplanin, blue; H3cit, red); in patient B (bottom), high levels of neutrophils in the lung corresponded to extensive intralymphatic fibrin clots and high levels of intralymphatic NETs in the LDLNs. (E-F) The density of neutrophils in the lungs correlates with lymphatic clotting in the LDLN of COVID-19 decedents. Linear regression correlations of (F) percentage of clotted LDLN lymphatic vessels (fibrin score 3-4) vs lung neutrophil density and (G) percentage of clotted LDLN lymphatic vessels vs lung NETs density. Scale bars, 100 μm (A,E).