Separate Immune Damage in TB and HIV Revealed in Tissues

Tuberculosis (TB) and HIV are two infections that, when present together, cause deep disruption of the immune system. Researchers led by Stephen Cose investigated exactly how these infections change the presence of key immune cells not only in the blood but also inside tissues where infection and immune defense actually take place. The team compared people with pulmonary TB, disseminated TB, HIV alone, and those with both TB and HIV. To do this they collected multiple sample types — peripheral blood mononuclear cells (PBMCs), lung tissue, bronchoalveolar lavage (BAL), spleen, and lung-draining hilar lymph nodes (HLN) — and measured immune cells directly in those compartments. The focus was on CD4⁺ and CD8⁺ T cells, B cells, and the specialized tissue-resident memory (TRM) forms of T and B cells that live in organs and provide localized protection. By looking at these cells across blood and relevant tissues, the study aimed to paint a clearer picture of how TB and HIV reshape immune defenses in the places that matter most for infection and recovery.

The central laboratory tool used was Flow cytometry to count and compare cell frequencies across compartments. Samples included PBMCs, lung tissue, BAL, spleen, and HLN from people grouped by disease status: pulmonary TB (PTB), disseminated TB (Diss TB), HIV only, or both TB and HIV. Key findings were compartment-specific. CD4⁺ T cell frequencies were significantly reduced in multiple compartments of HIV-infected subjects, independent of whether they also had TB, indicating broad CD4⁺ loss tied to HIV. In contrast, CD8⁺ T-cell frequencies were higher in the blood of HIV-infected individuals, a change the authors interpret as a likely compensatory response to CD4⁺ T-cell depletion. B-cell frequencies were lower in PBMCs and lung tissue of TB subjects regardless of HIV status. Importantly, tissue-resident memory subsets showed distinct patterns: CD4⁺ TRM T cells were specifically depleted in lung tissue of people with both HIV and TB, while TRM B cells were selectively depleted in TB subjects whether or not they had HIV. These results show separate effects on TRM populations depending on the pathogen and location.

The study’s findings highlight that TB and HIV do not simply cause the same kind of immune damage everywhere; instead, each infection targets different types of tissue-resident immunity in particular compartments. HIV primarily erodes CD4⁺ T-cell populations broadly and specifically hits CD4⁺ TRM T cells in the lung when co-infection occurs, while TB is associated with loss of TRM B cells in affected tissues independent of HIV. This separation suggests distinct biological mechanisms of tissue immune disruption for the two pathogens and underscores why blood tests alone can miss important local immune deficits. For vaccine designers and developers of immunotherapies, the message is clear: strategies should account for tissue-resident populations and the specific cell types each pathogen affects. Targeting or protecting TRM B cells for TB and preserving or restoring CD4⁺ TRM T cells in the lungs for people with HIV may be important directions, and the work supports greater emphasis on sampling and analyzing tissues, not just blood, in future clinical studies.