Pati BK, Panda PK. Body size and infection: An immunological balancing act. World J Immunol 2026; 16(2): 114815 [DOI: 10.5411/wji.v16.i2.114815]
Corresponding Author of This Article
Prasan Kumar Panda, Professor, Department of Medicine, All India Institute of Medical Sciences, Room No. 409, Building No 1, Rishikesh 249203, India. motherprasanna@rediffmail.com
Research Domain of This Article
Infectious Diseases
Article-Type of This Article
Opinion Review
Open-Access Policy of This Article
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World J Immunol. Feb 12, 2026; 16(2): 114815 Published online Feb 12, 2026. doi: 10.5411/wji.v16.i2.114815
Body size and infection: An immunological balancing act
Binod Kumar Pati, Prasan Kumar Panda
Binod Kumar Pati, Department of Microbiology, All India Institute of Medical Sciences, Bihar 801507, India
Prasan Kumar Panda, Department of Medicine, All India Institute of Medical Sciences, Rishikesh 249203, India
Author contributions: Pati BK and Panda PK designed the research study, performed the research, contributed analytic tools, analyzed the data and wrote the manuscript. All authors have read and approved the final manuscript.
Conflict-of-interest statement: All the authors report no relevant conflicts of interest for this article.
Corresponding author: Prasan Kumar Panda, Professor, Department of Medicine, All India Institute of Medical Sciences, Room No. 409, Building No 1, Rishikesh 249203, India. motherprasanna@rediffmail.com
Received: September 29, 2025 Revised: October 23, 2025 Accepted: January 7, 2026 Published online: February 12, 2026 Processing time: 135 Days and 19.1 Hours
Abstract
The human immune system functions across a vast spectrum of biological scales, from nanometer-sized signaling molecules to meter-long organ systems. This scale diversity underpins the ability to maintain homeostasis while confronting pathogens of markedly different sizes. To explore how the size of pathogens and host defense mechanisms shape infection susceptibility, immune strategies, and evolutionary host-microbe dynamics, this narrative review synthesizes evidence from immunology, microbiology, and evolutionary biology to examine the influence of size at molecular, cellular, and anatomical levels. Key themes include pathogen niche specialization, structural and immune barriers, size mismatches leading to invasion, and evolutionary implications for infection control. Pathogen size dictates strategies of entry, persistence, and immune evasion - from the nanometric replication of viruses to the chronic modulation of immunity by helminths. Host defenses, including molecular mediators, phagocytes, and large-scale anatomical barriers, are scaled to counter these challenges. Disruptions in this hierarchy, such as barrier breaches or immunodeficiencies, predispose to characteristic infections. Moreover, evolutionary pressures linked to size drive microbial adaptation, including antimicrobial resistance, while shaping host tolerance and immunity. Recognizing the role of size as a determinant in host-pathogen interactions reframes infection as a scale-dependent dialogue. Integrating this perspective may inform precision medicine, microbiome engineering, and strategies to mitigate emerging threats such as antimicrobial resistance.
Core Tip: Pathogen and host dimensions - from nanometer molecules to meter-long structures - govern the strategies of infection, immunity, and survival. Nanometric viruses to larger helminths are countered by host defenses, such as molecular mediators, phagocytes, and anatomical barriers. Furthermore, time pressure links size driven microbial adaptation, including antimicrobial resistance, into host tolerance and immunity. Recognizing size as a central determinant in host-microbe interactions provides new insights into susceptibility, antimicrobial resistance, and opportunities for precision medicine.
