Pathogen-associated molecular patterns (PAMP) such as lipopolysaccharide (LPS), lipoteichoic acid, beta-glucans (BGL), and possibly many others are important parts of (fine) dust in animal houses. When intratracheally (i.t.) administered, PAMP affected specific primary and secondary humoral immune responses to concurrently i.t. or systemically administered antigens and BW gain (BWG) of layer chickens. In the present study, we evaluated the effects of i.t. challenge with various PAMP known to be present in dust: LPS, lipoteichoic acid, zymosan-A (containing 1,3 BGL), next to heat-inactivated dust particles as a representative of mechanical stress, a combination of the former components, and NH3 as a chemical component of dust on primary and secondary (total) systemic antibody (Ab) responses and (isotype) IgM and IgG responses to concurrently i.t.-administered human serum albumin (HuSA) in broilers. Birds were challenged via the trachea for 2 consecutive days at 3 and 7 wk of age, respectively. All treatments affected immune responses at several moments, BWG, and heart morphology. beta-Glucans and LPS affected the birds most pronounced and for a prolonged period. Intratracheally administered LPS and BGL significantly enhanced primary and secondary total Ab, IgM Ab, and IgG Ab responses to HuSA. All birds that were challenged with dust, PAMP, or NH3 concurrently with HuSA showed a decreased BWG especially after primary, but also after secondary challenge. Weight, width, and length of hearts were enhanced in dust and PAMP-treated birds as well when these birds were challenged with HuSA. The present results indicated that components of dust such as PAMP when i.t. administered affect humoral immune responsiveness of broilers, which may lead to an enhanced status of immune reactivity. Furthermore, our results suggest that the hygienic status of the environment influences BWG and may affect heart morphology, and as a consequence physiology in broilers. The consequences of our findings with respect to dust, (airborne) PAMP, hygienic conditions in the barn, and immune responsiveness of broilers are discussed.