Back to basics: host responses to infection.

Abstract

1. Armond S. Goldman, MD* 1. 2. *Department of Pediatrics, Division of Immunology/Allergy/Rheumatology, The University of Texas Medical Branch, Galveston, TX, USA. Dr. Goldman is the recipient of several small grants from Wyeth Nutritional International for research concerning bioactive factors in human milk. An understanding of host responses to infections is important to pediatricians for five major reasons: 1) The manifestations of infectious diseases are due not only to microbial pathogens but also to their interactions with the immune system of the host. 2) Both the type of immune response and the infecting agent dictates whether the disease will be acute or protracted. 3) Because the immune responses of the child are age-related, manifestations and outcomes of certain infections depend on the child’s developmental status. 4) The immune state of the infant is modified by maternal factors transferred during fetal life via the placenta and during infancy via the mammary gland. Therefore, resistance to infection is decreased if the duration or degree of placental transfer is decreased or if infants are not breastfed. These factors can be modified to some extent by pediatricians and their colleagues. 5) Because resistance to many common infections can be induced by immunizations, it is important for pediatricians to understand the immunologic strategies used to develop immunizing agents. In childhood, the external environment initially is encountered by the skin, the respiratory tract, and the alimentary tract. The skin defines the external limits of the organism, aids in temperature regulation, and is a site of insensible water loss. The respiratory tract regulates respiratory gas exchange and insensible water loss. The alimentary tract is responsible for ingestion, digestion, and absorption of nutrients; some insensible water loss; and excretion of waste products. Each of these vital systems is exposed to environmental pathogens. Innate and specific adaptive defenses have evolved to protect these vital structures and systemic sites that may become invaded if first lines of defense at the skin or mucosa fail (Table 1⇓ and Fig. 1⇓ ). View this table: Table 1. Major Features of Innate and Specific Adaptive Immunity ### INNATE DEFENSES Innate defenses are …