Single Doses of GSK3008348 in Idiopathic Pulmonary Fibrosis (IPF) Participants Using Positron Emission Tomography (PET) Imaging

Inclusion Criteria:

• Male participants aged >= 50 years, and female participants aged >=55 years, at the time of signing the informed consent.
• Diagnosis of definite or probable IPF as determined by a responsible and experienced chest physician and based on established criteria defined by the American Thoracic Society/European Respiratory Society Internationale Multidisciplinary Consensus Classification of the Idiopathic Interstitial Pneumonias.
• Ambulant and capable of attending outpatient visits.
• FVC > 50 percent predicted and DLCO > 40 percent predicted.
• Body weight >= 45 kilograms (kg) and body mass index (BMI) within the range 18.0-35.0 kg/square meter (inclusive).
• Male and female
• Male participants: A male participant must agree to use contraception as detailed in this protocol during the study and for at least 90 days after the follow up visit, and refrain from donating sperm during this period.
• Female participants: A female participant is eligible to participate if she is not pregnant, not breastfeeding, and not a woman of childbearing potential (WOCBP) as defined in the protocol.
• Capable of giving signed informed consent, which includes compliance with the requirements and restrictions, listed in the informed consent form (ICF) and in this protocol.

Exclusion Criteria:

• ALT and bilirubin > 1.5x upper limit of normal (ULN; isolated bilirubin > 1.5xULN is acceptable if bilirubin is fractionated and direct bilirubin < 35 percent).
• Current or chronic history of liver disease, or known hepatic or biliary abnormalities (with the exception of Gilbert's syndrome or asymptomatic gallstones).
• QT corrected (QTc) > 450 milliseconds (msec), or QTc > 480 msec in participants with Bundle Branch Block.
• Current IPF exacerbation, or upper or lower respiratory tract infection on admission to the clinical unit.
• History of or suffers from claustrophobia, or unable to lie flat and still on their back for up to 2 hrs in the PET scanner.
• Extent of emphysema greater than the extent of fibrotic change on High-Resolution Computed Tomography (HRCT) scan, based on investigator judgment.
• FEV1/FVC ratio < 0.70 at screening (post-bronchodilator).
• History of sensitivity to the study treatment, or components thereof, or a history of drug or other allergy that, in the opinion of the investigators or Medical Monitor, contraindicates their participation.
• Any current oro-pharygneal disease or disorders as judged by the investigator.
• Currently taking pirfenidone or nintedanib, or received pirfenidone or nintedanib within 30 days of the first dose of study treatment.
• Taken, within 7 days or 5 half-lives (whichever is longer) before the first dose of study treatment, organic anion transporter (OAT) substrates with a narrow therapeutic index (example: methotrexate and tenofovir), vitamins, or dietary or herbal supplements, unless in the opinion of the investigator and sponsor the supplement will not interfere with the study medication.
• Long-term continuous home oxygen therapy (use of oxygen that is only intermittent and for symptom relief is acceptable).
• Participation in a clinical trial and receipt of an investigational medicinal product within the following time period before the first dose in the current study: 30 days, 5 half-lives or twice the duration of the biological effect of the investigational product (whichever is longer).
• Exposure to more than 4 new investigational medicinal products within 12 months before the first dose.
• Presence of Hepatitis B surface antigen (HBsAg) at screening, or positive Hepatitis C antibody test result at screening or within 3 months before the first dose of study treatment.

Note: participants with a positive Hepatitis C antibody test because of previous, resolved disease can be enrolled if a confirmatory negative Hepatitis C Ribonucleic Acid (RNA) test is obtained.

• Previous or current exposure to animals that may harbour Food and Mouth Disease Virus (FMDV2).
• Previous long term (>= 3 months) residence in a country where FMDV2 is endemic (such as certain areas of Africa, Asia and South America.
• Where participation in the study would result in loss of blood or blood products in excess of 500 milliliter (mL) within 56 days.
• History of drug or alcohol abuse that in the opinion of the investigator affects their participation in the study.
• Exposure to ionizing radiation in excess of 10 Millisievert (mSv) above background over the previous 3 year period as a result of occupational exposure or previous participation in research studies. Clinically justified (therapeutic or diagnostic) exposures are not included in the exposure calculation.