Fig. 8. Mature CD138⁺ plasma cells are enriched in the lung tissue, resulting in an upregulated Mtb specific antibody response that enhances Mtb phagocytosis.

a The tissue residence marker CD69 was expressed on antibody-secreting cells (ASC), with the majority displaying a mature plasma cell CD138⁺ phenotype in both cancer controls (n = 8) and patients with TB (n = 13 to 25). b Antibodies were isolated from homogenised lung tissue supernatants using a thiophilic resin, with example elution profiles from five lungs measured at 280 nm, and then examined on a reducing 12.5% SDS-PAGE gel. The molecular weight marker (lane M), was followed by the initial lung homogenate supernatant sample (lane 1), the unbound sample (lane 2) followed by the eluted fractions 1–5 from the elution profile alongside (lanes 3–7). c Peak eluents (lane 1) were tested for the presence of IgM, IgD, IgG and IgA using class-specific secondary antibodies by western blot. d Mtb-specific antibody binding was investigated in lung samples from cancer controls (n = 6) and patients with TB (n = 10), detecting both total reactivity and e class-specific responses in a direct ELISA-based approach, expressed as area under the curve (AUC). An equal concentration range (100 to 0.8 µg/ml) of isolated antibody was used to standardize the assay and allow for comparison between patients. Antibody frequencies were compared by Mann–Whitney test. f Mtb phagocytosis by PBMCs was compared between untreated Mtb versus Mtb treated with non-specific immunoglobulin (NSIg) or lung immunoglobulin (LIg) from patients with TB. The lung-derived immunoglobulin increased phagocytosis, while non-specific immunoglobulin had no effect. Data are presented as summary data from five immunoglobulin samples from patients with TB, tested with three different PBMC donors, with each experiment done in quadruplicate and infectivity was measured by luminescence. Data were normalized to the media control and the donor matched mean differences were compared by one-way ANOVA. g Representative Mtb growth using immunoglobulin from patients with TB comparing with untreated and non-specific immunoglobulin in the 3D biomimetic model of TB. h Mtb luminescence at day 8 normalized to day 0 initial infectious load shows no overall difference in growth rate over time. P values are denoted by * ≤0.05; ** <0.01; *** <0.001 and **** <0.0001.