Tissue-Specific Immunity in Osteoarticular Tuberculosis

Area of Science:

• Immunology
• Orthopedics
• Infectious Diseases

Background:

• Osteoarticular tuberculosis (TB) accounts for approximately 10% of extrapulmonary TB cases.
• Its incidence is notably low, particularly in non-HIV patients, suggesting potential tissue-specific immunity.
• The mechanisms of immunity against TB in bone and joints are less understood compared to pulmonary TB.

Purpose of the Study:

• To analyze the concept of tissue-specific immunity in osteoarticular tuberculosis.
• To investigate factors contributing to the low incidence of TB in bones and joints.

Main Methods:

• A literature search was conducted across PubMed, EMBASE, and Cochrane databases for English-language studies from May 2000 to September 2020.
• Information from 24 selected studies was compiled and analyzed to understand tissue-specific immunity in osteoarticular TB.

Main Results:

• Bones receive a lower proportion of cardiac output compared to lungs, GI, and urinary systems, potentially reducing mycobacterial spread.
• The oxygen-depleted microenvironment in bones influences T-cell responses, contrasting with oxygen-replete lungs.
• Higher concentrations of CD4 cells in bone marrow may contribute to local immunity, despite variations observed in other tissues like lymph nodes.

Conclusions:

• Low incidence of osteoarticular TB may be attributed to reduced blood flow, an oxygen-depleted microenvironment, and high CD4 cell counts in bone.
• Further molecular-level research is required to fully elucidate the mechanisms of tissue-specific immunity in skeletal TB.