Objective To explore the expression characteristics of immunoglobulin heavy constant gamma 3 (IGHG3), NK cells, CD4+ T lymphocytes, and CD8+ T lymphocytes in pulmonary tuberculosis patients and their relationship with disease severity and prognosis. Methods A total of 105 patients with newly-diagnosed pulmonary tuberculosis were selected as the observation group, and 50 healthy individuals who underwent physical examination were selected as the control group. The TBscore method was used to evaluate the disease severity (classified as mild, moderate, or severe) of patients in the observation group; after standardized anti-tuberculosis treatment, their prognosis (classified as good prognosis or poor prognosis) was evaluated based on clinical symptoms, imaging findings, and negative conversion of etiological examination. Immunological indicators (serum IGHG3 level and peripheral blood NK cells, CD4+T lymphocytes, and CD8+T lymphocytes proportions) were compared between the observation group and the control group, as well as among patients with different disease severities and between patients with different prognoses in the observation group. Spearman rank correlation analysis was used to assess the correlations between immunological indicators and disease severity, as well as prognosis, in the observation group. Results The serum IGHG3 level and peripheral blood NK cells and CD8+T lymphocytes proportions in the observation group were higher than those in the control group, while the peripheral blood CD4+T lymphocytes proportion in the observation group was lower than that in the control group (all P<0.05). In the observation group, there were statistically significant overall differences in the serum IGHG3 level and the peripheral blood NK cells, CD4+T lymphocytes, and CD8+T lymphocytes proportions among patients with different disease severities (all P<0.05). Specifically, the serum IGHG3 level and peripheral blood NK cells and CD8+T lymphocytes proportions increased sequentially in patients with mild, moderate, and severe disease, while the CD4+T lymphocytes proportion decreased sequentially in the same order (all P<0.05). In the observation group, patients with poor prognosis had a higher serum IGHG3 level, increased peripheral blood NK cells and CD8+T lymphocytes proportions, and a lower CD4+T lymphocytes proportion compared with those with good prognosis (all P<0.05). Spearman rank correlation analysis showed that the serum IGHG3 level and peripheral blood NK cells and CD8+T lymphocytes proportions in pulmonary tuberculosis patients were positively correlated with disease severity and prognosis, while the CD4+T lymphocytes proportion was negatively correlated with disease severity and prognosis (all P<0.05). Conclusion In patients with pulmonary tuberculosis, the serum IGHG3 level and peripheral blood NK cells, and CD8+T lymphocytes proportions are elevated, while the CD4+T lymphocytes proportion is decreased. These changes are closely related to disease severity and poor prognosis in pulmonary tuberculosis patients. 

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